Link with --undefined-version
lld 16 defaults to --no-undefined-version but the version script can
contain symbols disabled by configuration options.
See #473.
diff --git a/configure.ac b/configure.ac
index 6edfec7..c6f627b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -466,6 +466,10 @@
AC_SUBST(VERSION_SCRIPT_FLAGS)
AM_CONDITIONAL([USE_VERSION_SCRIPT], [test -n "$VERSION_SCRIPT_FLAGS"])
+dnl lld 16 defaults to --no-undefined-version but the version script
+dnl can contain symbols disabled by configuration options.
+AX_APPEND_LINK_FLAGS([-Wl,--undefined-version], [AM_LDFLAGS])
+
dnl
dnl Workaround for native compilers
dnl HP : http://bugs.gnome.org/db/31/3163.html
diff --git a/m4/ax_append_flag.m4 b/m4/ax_append_flag.m4
new file mode 100644
index 0000000..dd6d8b6
--- /dev/null
+++ b/m4/ax_append_flag.m4
@@ -0,0 +1,50 @@
+# ===========================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_append_flag.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+# AX_APPEND_FLAG(FLAG, [FLAGS-VARIABLE])
+#
+# DESCRIPTION
+#
+# FLAG is appended to the FLAGS-VARIABLE shell variable, with a space
+# added in between.
+#
+# If FLAGS-VARIABLE is not specified, the current language's flags (e.g.
+# CFLAGS) is used. FLAGS-VARIABLE is not changed if it already contains
+# FLAG. If FLAGS-VARIABLE is unset in the shell, it is set to exactly
+# FLAG.
+#
+# NOTE: Implementation based on AX_CFLAGS_GCC_OPTION.
+#
+# LICENSE
+#
+# Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
+# Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com>
+#
+# Copying and distribution of this file, with or without modification, are
+# permitted in any medium without royalty provided the copyright notice
+# and this notice are preserved. This file is offered as-is, without any
+# warranty.
+
+#serial 8
+
+AC_DEFUN([AX_APPEND_FLAG],
+[dnl
+AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_SET_IF
+AS_VAR_PUSHDEF([FLAGS], [m4_default($2,_AC_LANG_PREFIX[FLAGS])])
+AS_VAR_SET_IF(FLAGS,[
+ AS_CASE([" AS_VAR_GET(FLAGS) "],
+ [*" $1 "*], [AC_RUN_LOG([: FLAGS already contains $1])],
+ [
+ AS_VAR_APPEND(FLAGS,[" $1"])
+ AC_RUN_LOG([: FLAGS="$FLAGS"])
+ ])
+ ],
+ [
+ AS_VAR_SET(FLAGS,[$1])
+ AC_RUN_LOG([: FLAGS="$FLAGS"])
+ ])
+AS_VAR_POPDEF([FLAGS])dnl
+])dnl AX_APPEND_FLAG
diff --git a/m4/ax_append_link_flags.m4 b/m4/ax_append_link_flags.m4
new file mode 100644
index 0000000..99b9fa5
--- /dev/null
+++ b/m4/ax_append_link_flags.m4
@@ -0,0 +1,44 @@
+# ===========================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_append_link_flags.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+# AX_APPEND_LINK_FLAGS([FLAG1 FLAG2 ...], [FLAGS-VARIABLE], [EXTRA-FLAGS], [INPUT])
+#
+# DESCRIPTION
+#
+# For every FLAG1, FLAG2 it is checked whether the linker works with the
+# flag. If it does, the flag is added FLAGS-VARIABLE
+#
+# If FLAGS-VARIABLE is not specified, the linker's flags (LDFLAGS) is
+# used. During the check the flag is always added to the linker's flags.
+#
+# If EXTRA-FLAGS is defined, it is added to the linker's default flags
+# when the check is done. The check is thus made with the flags: "LDFLAGS
+# EXTRA-FLAGS FLAG". This can for example be used to force the linker to
+# issue an error when a bad flag is given.
+#
+# INPUT gives an alternative input source to AC_COMPILE_IFELSE.
+#
+# NOTE: This macro depends on the AX_APPEND_FLAG and AX_CHECK_LINK_FLAG.
+# Please keep this macro in sync with AX_APPEND_COMPILE_FLAGS.
+#
+# LICENSE
+#
+# Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com>
+#
+# Copying and distribution of this file, with or without modification, are
+# permitted in any medium without royalty provided the copyright notice
+# and this notice are preserved. This file is offered as-is, without any
+# warranty.
+
+#serial 7
+
+AC_DEFUN([AX_APPEND_LINK_FLAGS],
+[AX_REQUIRE_DEFINED([AX_CHECK_LINK_FLAG])
+AX_REQUIRE_DEFINED([AX_APPEND_FLAG])
+for flag in $1; do
+ AX_CHECK_LINK_FLAG([$flag], [AX_APPEND_FLAG([$flag], [m4_default([$2], [LDFLAGS])])], [], [$3], [$4])
+done
+])dnl AX_APPEND_LINK_FLAGS
diff --git a/m4/ax_check_link_flag.m4 b/m4/ax_check_link_flag.m4
new file mode 100644
index 0000000..03a30ce
--- /dev/null
+++ b/m4/ax_check_link_flag.m4
@@ -0,0 +1,53 @@
+# ===========================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_check_link_flag.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+# AX_CHECK_LINK_FLAG(FLAG, [ACTION-SUCCESS], [ACTION-FAILURE], [EXTRA-FLAGS], [INPUT])
+#
+# DESCRIPTION
+#
+# Check whether the given FLAG works with the linker or gives an error.
+# (Warnings, however, are ignored)
+#
+# ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
+# success/failure.
+#
+# If EXTRA-FLAGS is defined, it is added to the linker's default flags
+# when the check is done. The check is thus made with the flags: "LDFLAGS
+# EXTRA-FLAGS FLAG". This can for example be used to force the linker to
+# issue an error when a bad flag is given.
+#
+# INPUT gives an alternative input source to AC_LINK_IFELSE.
+#
+# NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. Please keep this
+# macro in sync with AX_CHECK_{PREPROC,COMPILE}_FLAG.
+#
+# LICENSE
+#
+# Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
+# Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com>
+#
+# Copying and distribution of this file, with or without modification, are
+# permitted in any medium without royalty provided the copyright notice
+# and this notice are preserved. This file is offered as-is, without any
+# warranty.
+
+#serial 6
+
+AC_DEFUN([AX_CHECK_LINK_FLAG],
+[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
+AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_ldflags_$4_$1])dnl
+AC_CACHE_CHECK([whether the linker accepts $1], CACHEVAR, [
+ ax_check_save_flags=$LDFLAGS
+ LDFLAGS="$LDFLAGS $4 $1"
+ AC_LINK_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
+ [AS_VAR_SET(CACHEVAR,[yes])],
+ [AS_VAR_SET(CACHEVAR,[no])])
+ LDFLAGS=$ax_check_save_flags])
+AS_VAR_IF(CACHEVAR,yes,
+ [m4_default([$2], :)],
+ [m4_default([$3], :)])
+AS_VAR_POPDEF([CACHEVAR])dnl
+])dnl AX_CHECK_LINK_FLAGS
diff --git a/m4/ax_require_defined.m4 b/m4/ax_require_defined.m4
new file mode 100644
index 0000000..17c3eab
--- /dev/null
+++ b/m4/ax_require_defined.m4
@@ -0,0 +1,37 @@
+# ===========================================================================
+# https://www.gnu.org/software/autoconf-archive/ax_require_defined.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+# AX_REQUIRE_DEFINED(MACRO)
+#
+# DESCRIPTION
+#
+# AX_REQUIRE_DEFINED is a simple helper for making sure other macros have
+# been defined and thus are available for use. This avoids random issues
+# where a macro isn't expanded. Instead the configure script emits a
+# non-fatal:
+#
+# ./configure: line 1673: AX_CFLAGS_WARN_ALL: command not found
+#
+# It's like AC_REQUIRE except it doesn't expand the required macro.
+#
+# Here's an example:
+#
+# AX_REQUIRE_DEFINED([AX_CHECK_LINK_FLAG])
+#
+# LICENSE
+#
+# Copyright (c) 2014 Mike Frysinger <vapier@gentoo.org>
+#
+# Copying and distribution of this file, with or without modification, are
+# permitted in any medium without royalty provided the copyright notice
+# and this notice are preserved. This file is offered as-is, without any
+# warranty.
+
+#serial 2
+
+AC_DEFUN([AX_REQUIRE_DEFINED], [dnl
+ m4_ifndef([$1], [m4_fatal([macro ]$1[ is not defined; is a m4 file missing?])])
+])dnl AX_REQUIRE_DEFINED
