Handle some compiler versions containing a dash

The version reported by e.g. x86_64-w64-mingw32-gcc on Debian bullseye
looks like:
  gcc version 10-win32 20210110 (GCC)

This ends up with detect-compiler failing with:
  ./detect-compiler: 30: test: Illegal number: 10-win32

This change removes the two known suffixes known to exist in GCC versions
in Debian: -win32 and -posix.

Signed-off-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

detect-compiler

@@ -17,7 +17,15 @@ get_family() {
 }
 
 get_version() {
-	get_version_line | sed 's/^.* version \([0-9][^ ]*\).*/\1/'
+	# A string that begins with a digit up to the next SP
+	ver=$(get_version_line | sed 's/^.* version \([0-9][^ ]*\).*/\1/')
+
+	# There are known -variant suffixes that do not affect the
+	# meaning of the main version number.  Strip them.
+	ver=${ver%-win32}
+	ver=${ver%-posix}
+
+	echo "$ver"
 }
 
 print_flags() {