regex: port to mingw's recent addition of undeclared alarm On mingw (at least, when cross-compiling with Fedora 18's mingw32-headers-2.0.999-0.15.trunk.20121110.fc18.noarch build), compilation of test-regex fails: test-regex.c: In function 'main': test-regex.c:42:11: error: 'SIGALRM' undeclared (first use in this function) test-regex.c:42:11: note: each undeclared identifier is reported only once for each function it appears in test-regex.c:43:3: warning: implicit declaration of function 'alarm' It turns out that recent mingw64 added an export of alarm() and SIGALRM, but guarded their declarations behind __USE_MINGW_ALARM (default off, and with alarm() only in the non-standard <io.h>); so the m4 tests were setting HAVE_ALARM to 1 based on link success but then failing to compile. * doc/posix-functions/alarm.texi (alarm): Document that alarm exists but still doesn't work in newer mingw. * m4/frexp.m4 (gl_FUNC_FREXP_WORKS): Check for alarm declaration, not existence. Ensure SIGALRM is not trapped. * m4/mktime.m4 (gl_FUNC_MKTIME): Likewise. * m4/regex.m4 (gl_REGEX): Likewise. * m4/remainderf.m4 (gl_FUNC_REMAINDERF_WORKS): Likewise. * tests/test-regex.c (main): Use correct probe for alarm. Signed-off-by: Eric Blake <eblake@redhat.com>

--- a/m4/remainderf.m4
+++ b/m4/remainderf.m4
@@ -1,4 +1,4 @@
-# remainderf.m4 serial 7
+# remainderf.m4 serial 8
 dnl Copyright (C) 2012-2013 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -150,13 +150,14 @@
 [
   AC_REQUIRE([AC_PROG_CC])
   AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
-  AC_CHECK_FUNCS_ONCE([alarm])
+  AC_CHECK_DECLS_ONCE([alarm])
   AC_CACHE_CHECK([whether remainderf works], [gl_cv_func_remainderf_works],
     [
       AC_RUN_IFELSE(
         [AC_LANG_SOURCE([[
 #include <math.h>
-#if HAVE_ALARM
+#if HAVE_DECL_ALARM
+# include <signal.h>
 # include <unistd.h>
 #endif
 extern
@@ -169,7 +170,8 @@
 float z;
 int main ()
 {
-#if HAVE_ALARM
+#if HAVE_DECL_ALARM
+  signal (SIGALRM, SIG_DFL);
   alarm (5);
 #endif
   /* This test fails on IRIX 6.5.  */