manywarnings: Fix for compilers that are named '$host-gcc'

Building a current gettext on Cygwin 2.9.0, with CC=x86_64-pc-cygwin-gcc,
I see many warnings like

cc1: warning: command line option ‘-Wuseless-cast’ is valid for C++/ObjC++ but not for C
cc1: warning: command line option ‘-Wzero-as-null-pointer-constant’ is valid for C++/ObjC++ but not for C

$CC --version is

"x86_64-pc-cygwin-gcc (GCC) 6.4.0
Copyright ..."

The problem is that manywarnings.m4 understands only gcc binaries installed
under the name "gcc" or "gcc-<version>" or something like that. This patch
fixes it.


2026-06-25  Bruno Haible  <[email protected]>

	manywarnings: Fix for compilers that are named '$host-gcc'.
	* m4/manywarnings.m4 (gl_MANYWARN_ALL_GCC(C)): Use only the first line
	of `$CC --version`. Allow $CC to be of the form '$host-gcc'.

diff --git a/m4/manywarnings.m4 b/m4/manywarnings.m4
index 1a50006245..6b323ba01d 100644
--- a/m4/manywarnings.m4
+++ b/m4/manywarnings.m4
@@ -1,5 +1,5 @@
 # manywarnings.m4
-# serial 35
+# serial 36
 dnl Copyright (C) 2008-2026 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -169,36 +169,39 @@ AC_DEFUN([gl_MANYWARN_ALL_GCC(C
   AS_VAR_APPEND([$1], [' -Wvla-larger-than=4031'])
 
   # These depend on the GCC version.
-  if test -n "$GCC" && gl_gcc_version=`($CC --version) 2>/dev/null`; then
+  if test -n "$GCC" \
+     && gl_gcc_version=`($CC --version) 2>/dev/null | sed 1q`; then
     case $gl_gcc_version in
-      gcc*' ('*') '[[0-3]].* | \
-      gcc*' ('*') '4.[[0-7]].*)
+      *gcc*' ('*') '[[0-3]].* | \
+      *gcc*' ('*') '4.[[0-7]].*)
         AS_VAR_APPEND([$1], [' -fdiagnostics-show-option'])
         AS_VAR_APPEND([$1], [' -funit-at-a-time'])
-          ;;
+        ;;
     esac
     case $gl_gcc_version in
-      gcc*' ('*') '[[0-9]].*)
+      *gcc*' ('*') '[[0-9]].*)
+        # In GCC >= 10 this option is no longer needed, as it is
+        # enabled by default.
         AS_VAR_APPEND([$1], [' -fno-common'])
-          ;;
+        ;;
     esac
     case $gl_gcc_version in
-      gcc*' ('*') '?.* | gcc*' ('*') '1[[0-3]].*)
-          # In GCC < 14 the option either does not exist,
-          # or is accepted but always warns.
-          ;;
+      *gcc*' ('*') '?.* | gcc*' ('*') '1[[0-3]].*)
+        # In GCC < 14 the option either does not exist,
+        # or is accepted but always warns.
+        ;;
       *)
-          AS_VAR_APPEND([$1], [' -Wuseless-cast'])
-          ;;
+        AS_VAR_APPEND([$1], [' -Wuseless-cast'])
+        ;;
     esac
     case $gl_gcc_version in
-      gcc*' ('*') '?.* | gcc*' ('*') '1[[0-4]].*)
-          # In GCC < 15 the option either does not exist,
-          # or is accepted but always warns.
-          ;;
+      *gcc*' ('*') '?.* | gcc*' ('*') '1[[0-4]].*)
+        # In GCC < 15 the option either does not exist,
+        # or is accepted but always warns.
+        ;;
       *)
-          AS_VAR_APPEND([$1], [' -Wzero-as-null-pointer-constant'])
-          ;;
+        AS_VAR_APPEND([$1], [' -Wzero-as-null-pointer-constant'])
+        ;;
     esac
   fi