fix gcc makefile

gcc_plugin/GNUmakefile

@@ -28,11 +28,11 @@ MAN_PATH    ?= $(PREFIX)/man/man8
 
 VERSION     = $(shell grep '^$(HASH)define VERSION ' ../config.h | cut -d '"' -f2)
 
-CFLAGS      ?= -O3 -g -funroll-loops -D_FORTIFY_SOURCE=2
-CFLAGS      += -Wall -I../include -Wno-pointer-sign \
-               -DAFL_PATH=\"$(HELPER_PATH)\" -DBIN_PATH=\"$(BIN_PATH)\" \
-               -DGCC_VERSION=\"$(GCCVER)\" -DGCC_BINDIR=\"$(GCCBINDIR)\" \
-               -Wno-unused-function
+CFLAGS          ?= -O3 -g -funroll-loops -D_FORTIFY_SOURCE=2
+override CFLAGS += -Wall -I../include -Wno-pointer-sign \
+                   -DAFL_PATH=\"$(HELPER_PATH)\" -DBIN_PATH=\"$(BIN_PATH)\" \
+                   -DGCC_VERSION=\"$(GCCVER)\" -DGCC_BINDIR=\"$(GCCBINDIR)\" \
+                   -Wno-unused-function
 
 CXXFLAGS    ?= -O3 -g -funroll-loops -D_FORTIFY_SOURCE=2
 CXXEFLAGS   := $(CXXFLAGS) -Wall
@@ -60,12 +60,12 @@ ifeq "$(shell echo '$(HASH)include <sys/ipc.h>@$(HASH)include <sys/shm.h>@int ma
 	SHMAT_OK=1
 else
 	SHMAT_OK=0
-	CFLAGS+=-DUSEMMAP=1
+	override CFLAGS += -DUSEMMAP=1
 endif
 
 ifeq "$(TEST_MMAP)" "1"
 	SHMAT_OK=0
-	CFLAGS+=-DUSEMMAP=1
+	override CFLAGS += -DUSEMMAP=1
 endif
 
 ifneq "$(shell uname -s)" "Haiku"