[libunwind] Support building hermetic static library

This is useful when the static libunwind library is being linked into
shared libraries that may be used in with other shared libraries that
use different unwinder. We want to avoid avoid exporting libunwind
symbols in those cases. This achieved by a new CMake option which can be
enabled by libunwind vendors as needed.

The same CMake option has already been added to libc++ and libc++abi in
D55404 and D56026.

Differential Revision: https://reviews.llvm.org/D57107

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@352559 91177308-0d34-0410-b5e6-96231b3b80d8

src/CMakeLists.txt

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 77722e6..246cfd8 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -218,7 +218,11 @@
 if (LIBCXXABI_ENABLE_STATIC)
   if (LIBCXXABI_USE_LLVM_UNWINDER AND LIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY)
     if (TARGET unwind_static OR HAVE_LIBUNWIND)
-      list(APPEND cxxabi_static_sources $<TARGET_OBJECTS:unwind_objects>)
+      if(LIBUNWIND_HERMETIC_STATIC_LIBRARY)
+        list(APPEND cxxabi_static_sources $<TARGET_OBJECTS:unwind_static_objects>)
+      else()
+        list(APPEND cxxabi_static_sources $<TARGET_OBJECTS:unwind_objects>)
+      endif()
     endif()
   endif()
   add_library(cxxabi_static STATIC ${cxxabi_static_sources})