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/frexp.m4
+++ b/m4/frexp.m4
@@ -1,4 +1,4 @@
-# frexp.m4 serial 14
+# frexp.m4 serial 15
 dnl Copyright (C) 2007-2013 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -93,7 +93,7 @@
 [
   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 frexp works], [gl_cv_func_frexp_works],
     [
       AC_RUN_IFELSE(
@@ -101,7 +101,8 @@
 #include <float.h>
 #include <math.h>
 #include <string.h>
-#if HAVE_ALARM
+#if HAVE_DECL_ALARM
+# include <signal.h>
 # include <unistd.h>
 #endif
 /* HP cc on HP-UX 10.20 has a bug with the constant expression -0.0.
@@ -124,9 +125,10 @@
   int i;
   volatile double x;
   double zero = 0.0;
-#if HAVE_ALARM
+#if HAVE_DECL_ALARM
   /* NeXTstep 3.3 frexp() runs into an endless loop when called on an infinite
      number.  Let the test fail in this case.  */
+  signal (SIGALRM, SIG_DFL);
   alarm (5);
 #endif
   /* Test on denormalized numbers.  */