Suggested by Jake Page <jake at cs dot stanford dot edu>

 in http://sources.redhat.com/ml/crossgcc/2004-07/msg00169.html

 but the libc-symbols.h fragment has been reworked to fix typos

 and to still work on gcc-2.95.3, which lacks _Pragma.

 His comment was:

  Fixes gcc-3.4 optimizing out comparisons to weak external symbols in code

  like:

   if (__pthread_mutex_init != NULL)

     __pthread_mutex_init(...);

  that causes segfaults during libc init when not linked to libpthread

 diff -uNr glibc-2.2.5-orig/resolv/res_libc.c glibc-2.2.5/resolv/res_libc.c

 --- glibc-2.2.5-orig/resolv/res_libc.c	2001-02-12 12:23:34.000000000 -0800

 +++ glibc-2.2.5/resolv/res_libc.c	2004-07-27 22:56:32.000000000 -0700

 @@ -84,7 +84,8 @@

  #if SHLIB_COMPAT(libc, GLIBC_2_0, GLIBC_2_2)

  # undef res_init

 -strong_alias (__res_init, __res_init_weak);

 +extern int __res_init_weak (void);

  weak_extern (__res_init_weak);

 +strong_alias (__res_init, __res_init_weak);

  compat_symbol (libc, __res_init_weak, res_init, GLIBC_2_0);

  #endif

 --- glibc-2.2.5/include/libc-symbols.h.old	Fri Aug 13 04:20:55 2004

 +++ glibc-2.2.5/include/libc-symbols.h	Fri Aug 13 04:37:06 2004

 @@ -108,10 +108,16 @@

  /* Declare SYMBOL as weak undefined symbol (resolved to 0 if not defined).  */

  #  define weak_extern(symbol) _weak_extern (symbol)

 -#  ifdef HAVE_ASM_WEAKEXT_DIRECTIVE

 -#   define _weak_extern(symbol) asm (".weakext " __SYMBOL_PREFIX #symbol);

 -#  else

 -#   define _weak_extern(symbol)    asm (".weak " __SYMBOL_PREFIX #symbol);

 +#  if __GNUC__ >= 3

 +    /* see http://sources.redhat.com/ml/libc-alpha/2003-01/msg00043.html */

 +#   define __weak_extern_1(expr) _Pragma(#expr)

 +#   define _weak_extern(symbol) __weak_extern_1(weak symbol)

 +#  else /* __GNUC__ == 2 */

 +#   ifdef HAVE_ASM_WEAKEXT_DIRECTIVE

 +#    define _weak_extern(symbol) asm (".weakext " __SYMBOL_PREFIX #symbol);

 +#   else

 +#    define _weak_extern(symbol)    asm (".weak " __SYMBOL_PREFIX #symbol);

 +#   endif

  #  endif

  # else