fdo#65124 define HAVE_FMERGENEUTRALITEMS for MSVC build

It has been added because mingw headers are missing
fMergeNeutralItems in SCRIPT_CONTROL struct
(see commit f6deda85),
so there is no apparent reason to disable it for MSVC.
It also resolves fdo#65124.

Change-Id: I4b7381f076c213f12f32cf03e2c0f321ccb1c4ce
Reviewed-on: https://gerrit.libreoffice.org/6711Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>

configure.ac

@@ -5665,6 +5665,10 @@ using namespace std;
     AC_SUBST(MINGW_GXXDLL)
 fi
 
+if test "$_os" = "WINNT" -a "$WITH_MINGW" != "yes"; then
+    AC_DEFINE(HAVE_FMERGENEUTRALITEMS)
+fi
+
 if test "$WITH_MINGW" = "yes"; then
     AC_MSG_CHECKING([for fMergeNeutralItems in SCRIPT_CONTROL])
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM(