Make Clang version detection work for clang-cl

...which does not behave as expected with the given command line arguments, so
just strip "-cl.exe" (and any hard-coded command line arguments following it in
$CC, but that's probably rather harmless here).  Expects that clang-cl is given
with an ".exe" extension in $CC (not assuming that and stripping "-cl" and
everything that might follow could be a bit too agressive).

Change-Id: If99f964dda1369b7d4bbb63b3d634b93c9f935a8

configure.ac

@@ -3762,8 +3762,8 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
 
 if test "$COM_IS_CLANG" = TRUE; then
     AC_MSG_CHECKING([the Clang version])
-    clang_version=`echo __clang_major__.__clang_minor__.__clang_patchlevel__ | $CC -E -P -`
-    CLANG_FULL_VERSION=`echo __clang_version__ | $CC -E -P -`
+    clang_version=`echo __clang_major__.__clang_minor__.__clang_patchlevel__ | ${CC%-cl.exe*} -E -P -`
+    CLANG_FULL_VERSION=`echo __clang_version__ | ${CC%-cl.exe*} -E -P -`
     CLANGVER=`echo $clang_version | $AWK -F. '{ print \$1*10000+\$2*100+\$3 }'`
     AC_MSG_RESULT([Clang $CLANG_FULL_VERSION, $CLANGVER])
     AC_DEFINE_UNQUOTED(CLANG_FULL_VERSION,$CLANG_FULL_VERSION)