--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2010-04-05  Bruno Haible  <bruno@clisp.org>
+
+	Make the multithread modules work on Cygwin 1.7.2.
+	* m4/threadlib.m4 (gl_THREADLIB_BODY): Improve the test whether
+	imported symbols can be declared weak, so that it returns "no" on
+	Cygwin 1.7.2.
+
 2010-04-05  Bruno Haible  <bruno@clisp.org>
 
 	Use the module 'strncat'.

--- a/m4/threadlib.m4
+++ b/m4/threadlib.m4
@@ -1,4 +1,4 @@
-# threadlib.m4 serial 4 (gettext-0.18)
+# threadlib.m4 serial 5 (gettext-0.18)
 dnl Copyright (C) 2005-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -107,11 +107,34 @@
   LTLIBMULTITHREAD=
   if test "$gl_use_threads" != no; then
     dnl Check whether the compiler and linker support weak declarations.
-    AC_MSG_CHECKING([whether imported symbols can be declared weak])
-    gl_have_weak=no
-    AC_TRY_LINK([extern void xyzzy ();
-#pragma weak xyzzy], [xyzzy();], [gl_have_weak=yes])
-    AC_MSG_RESULT([$gl_have_weak])
+    AC_CACHE_CHECK([whether imported symbols can be declared weak],
+      [gl_cv_have_weak],
+      [gl_cv_have_weak=no
+       dnl First, test whether the compiler accepts it syntactically.
+       AC_TRY_LINK([extern void xyzzy ();
+#pragma weak xyzzy], [xyzzy();], [gl_cv_have_weak=maybe])
+       if test $gl_cv_have_weak = maybe; then
+         dnl Second, test whether it actually works. On Cygwin 1.7.2, with
+         dnl gcc 4.3, symbols declared weak always evaluate to the address 0.
+         AC_TRY_RUN([
+#include <stdio.h>
+#pragma weak fputs
+int main ()
+{
+  return (fputs == NULL);
+}], [gl_cv_have_weak=yes], [gl_cv_have_weak=no],
+           [dnl When cross-compiling, assume that only ELF platforms support
+            dnl weak symbols.
+            AC_EGREP_CPP([Extensible Linking Format],
+              [#ifdef __ELF__
+               Extensible Linking Format
+               #endif
+              ],
+              [gl_cv_have_weak="guessing yes"],
+              [gl_cv_have_weak="guessing no"])
+           ])
+       fi
+      ])
     if test "$gl_use_threads" = yes || test "$gl_use_threads" = posix; then
       # On OSF/1, the compiler needs the flag -pthread or -D_REENTRANT so that
       # it groks <pthread.h>. It's added above, in gl_THREADLIB_EARLY_BODY.
@@ -165,7 +188,7 @@
           AC_DEFINE([USE_POSIX_THREADS], [1],
             [Define if the POSIX multithreading library can be used.])
           if test -n "$LIBMULTITHREAD" || test -n "$LTLIBMULTITHREAD"; then
-            if test $gl_have_weak = yes; then
+            if case "$gl_cv_have_weak" in *yes) true;; *) false;; esac; then
               AC_DEFINE([USE_POSIX_THREADS_WEAK], [1],
                 [Define if references to the POSIX multithreading library should be made weak.])
               LIBTHREAD=
@@ -193,7 +216,7 @@
           LTLIBMULTITHREAD="$LTLIBTHREAD"
           AC_DEFINE([USE_SOLARIS_THREADS], [1],
             [Define if the old Solaris multithreading library can be used.])
-          if test $gl_have_weak = yes; then
+          if case "$gl_cv_have_weak" in *yes) true;; *) false;; esac; then
             AC_DEFINE([USE_SOLARIS_THREADS_WEAK], [1],
               [Define if references to the old Solaris multithreading library should be made weak.])
             LIBTHREAD=
@@ -219,7 +242,7 @@
         AC_DEFINE([USE_PTH_THREADS], [1],
           [Define if the GNU Pth multithreading library can be used.])
         if test -n "$LIBMULTITHREAD" || test -n "$LTLIBMULTITHREAD"; then
-          if test $gl_have_weak = yes; then
+          if case "$gl_cv_have_weak" in *yes) true;; *) false;; esac; then
             AC_DEFINE([USE_PTH_THREADS_WEAK], [1],
               [Define if references to the GNU Pth multithreading library should be made weak.])
             LIBTHREAD=