This patch is one of the motivating reasons for upgrading glibc from 2.15.

Unfortunately, we couldn't upgrade to 2.19(*) due to some users having 2.17.

* - which no longer needs the patch, since the #ifdefs around __gnu_inline__ are
    worded so that compilers that don't have __GNUC_PREREQ(4, 3) can still get
    the reasonable definition for __gnu_inline__

-----
diff --git a/amd64/usr/include/x86_64-linux-gnu/sys/cdefs.h b/amd64/usr/include/x86_64-linux-gnu/sys/cdefs.h
index fb6c959..bd9ee92 100644
--- a/usr/include/x86_64-linux-gnu/sys/cdefs.h
+++ b/usr/include/x86_64-linux-gnu/sys/cdefs.h
@@ -320,7 +320,7 @@
 
 /* GCC 4.3 and above with -std=c99 or -std=gnu99 implements ISO C99
    inline semantics, unless -fgnu89-inline is used.  */
-#if (!defined __cplusplus || __GNUC_PREREQ (4,3)) && defined __GNUC__
+#if (!defined __cplusplus || __GNUC_PREREQ (4,3) || defined __clang__) && defined __GNUC__
 # if defined __GNUC_STDC_INLINE__ || defined __cplusplus
 #  define __extern_inline extern __inline __attribute__ ((__gnu_inline__))
 #  define __extern_always_inline \
diff --git a/i386/usr/include/i386-linux-gnu/sys/cdefs.h b/i386/usr/include/i386-linux-gnu/sys/cdefs.h
index fb6c959..bd9ee92 100644
--- a/usr/include/i386-linux-gnu/sys/cdefs.h
+++ b/usr/include/i386-linux-gnu/sys/cdefs.h
@@ -320,7 +320,7 @@
 
 /* GCC 4.3 and above with -std=c99 or -std=gnu99 implements ISO C99
    inline semantics, unless -fgnu89-inline is used.  */
-#if (!defined __cplusplus || __GNUC_PREREQ (4,3)) && defined __GNUC__
+#if (!defined __cplusplus || __GNUC_PREREQ (4,3) || defined __clang__) && defined __GNUC__
 # if defined __GNUC_STDC_INLINE__ || defined __cplusplus
 #  define __extern_inline extern __inline __attribute__ ((__gnu_inline__))
 #  define __extern_always_inline \