fix which files -DIN_GCC_FRONTEND is applied to

Author: mrgtwentythree

external/gpl3/gcc/usr.bin/Makefile.frontend

@@ -1,10 +1,9 @@
-#	$NetBSD: Makefile.frontend,v 1.7 2019/10/24 18:48:43 christos Exp $
+#	$NetBSD: Makefile.frontend,v 1.8 2026/01/18 08:51:07 mrg Exp $
 
 BINDIR=		/usr/bin
 
 CPPFLAGS+=	-I${GCCARCH} -I${FRONTENDOBJ} \
-		${G_ALL_CFLAGS:M-D*} ${G_INCLUDES:M-I*:N-I.*} \
-		-DIN_GCC_FRONTEND
+		${G_ALL_CFLAGS:M-D*} ${G_INCLUDES:M-I*:N-I.*}
 
 NOCTF=		# defined
 .include <bsd.init.mk>

external/gpl3/gcc/usr.bin/Makefile.inc

@@ -1,4 +1,4 @@
-#	$NetBSD: Makefile.inc,v 1.42 2025/10/20 14:31:37 nat Exp $
+#	$NetBSD: Makefile.inc,v 1.43 2026/01/18 08:51:07 mrg Exp $
 
 .ifndef _EXTERNAL_GPL3_GCC_USR_BIN_MAKEFILE_INC_
 _EXTERNAL_GPL3_GCC_USR_BIN_MAKEFILE_INC_=1
@@ -78,6 +78,10 @@ CPPFLAGS+=	-DNO_SHARED_LIBGCC_MULTILIB
 .endif
 .endif
 
+.for _f in ${G_ALL_HOST_FRONTEND_OBJS:.o=.cc}
+COPTS.${_f}+=	-DIN_GCC_FRONTEND
+.endfor
+
 NOCLANGERROR=	# defined
 
 WARNS=1