https://github.com/tianocore/edk2/commit/e063f8b8a53861043b9872cc35b08a3dc03b0942
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Mon, 20 Jan 2025 09:40:31 +0100
Subject: [PATCH] BaseTools/Pccts: set C standard

The prehistoric code base doesn't build with ISO C23.  Set the C
standard to C11 (for both clang and gcc) so it continues to build with
gcc 15 (which uses C23 by default).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
--- a/BaseTools/Source/C/VfrCompile/Pccts/antlr/makefile
+++ b/BaseTools/Source/C/VfrCompile/Pccts/antlr/makefile
@@ -169,7 +169,7 @@ ANTLR=${BIN_DIR}/antlr
 DLG=${BIN_DIR}/dlg
 OBJ_EXT=o
 OUT_OBJ = -o
-CFLAGS= $(COPT) -I. -I$(SET) -I$(PCCTS_H) -DUSER_ZZSYN $(COTHER) -DZZLEXBUFSIZE=65536
+CFLAGS= $(COPT) -I. -I$(SET) -I$(PCCTS_H) -DUSER_ZZSYN $(COTHER) -DZZLEXBUFSIZE=65536 -std=gnu11
 CPPFLAGS=
 #
 # SGI Users, use this CFLAGS
--- a/BaseTools/Source/C/VfrCompile/Pccts/dlg/makefile
+++ b/BaseTools/Source/C/VfrCompile/Pccts/dlg/makefile
@@ -123,7 +123,7 @@ endif
 COPT=-O
 ANTLR=${BIN_DIR}/antlr
 DLG=${BIN_DIR}/dlg
-CFLAGS= $(COPT) -I. -I$(SET) -I$(PCCTS_H) -DUSER_ZZSYN -DZZLEXBUFSIZE=65536
+CFLAGS= $(COPT) -I. -I$(SET) -I$(PCCTS_H) -DUSER_ZZSYN -DZZLEXBUFSIZE=65536 -std=gnu11
 CPPFLAGS=
 OBJ_EXT=o
 OUT_OBJ = -o