Give user's compiler flags precedence over default ones

The user can provide additional CFLAGS to use when building TF.
However, these custom CFLAGS are currently prepended to the
standard CFLAGS that are hardcoded in the TF build system. This
is an issue because when providing conflicting compiler flags
(e.g. different optimisations levels like -O1 and -O0), the last
one on the command line usually takes precedence. This means that
the user flags get overriden.

To address this problem, this patch separates the TF CFLAGS from
the user CFLAGS. The former are now stored in the TF_CFLAGS make
variable, whereas the CFLAGS make variable is untouched and reserved
for the user. The order of the 2 sets of flags is enforced when
invoking the compiler.

Fixes ARM-Software/tf-issues#350

Change-Id: Ib189f44555b885f1dffbec6015092f381600e560

Makefile

@@ -136,7 +136,7 @@ export Q
 $(eval $(call add_define,DEBUG))
 ifneq (${DEBUG}, 0)
         BUILD_TYPE	:=	debug
-        CFLAGS		+= 	-g
+        TF_CFLAGS	+= 	-g
         ASFLAGS		+= 	-g -Wa,--gdwarf-2
         # Use LOG_LEVEL_INFO by default for debug builds
         LOG_LEVEL	:=	40
@@ -179,12 +179,12 @@ ASFLAGS			+= 	-nostdinc -ffreestanding -Wa,--fatal-warnings	\
 				-Werror -Wmissing-include-dirs			\
 				-mgeneral-regs-only -D__ASSEMBLY__		\
 				${DEFINES} ${INCLUDES}
-CFLAGS			+= 	-nostdinc -ffreestanding -Wall			\
+TF_CFLAGS		+= 	-nostdinc -ffreestanding -Wall			\
 				-Werror -Wmissing-include-dirs			\
 				-mgeneral-regs-only -mstrict-align		\
 				-std=c99 -c -Os					\
 				${DEFINES} ${INCLUDES}
-CFLAGS			+=	-ffunction-sections -fdata-sections
+TF_CFLAGS		+=	-ffunction-sections -fdata-sections
 
 LDFLAGS			+=	--fatal-warnings -O1
 LDFLAGS			+=	--gc-sections
@@ -331,7 +331,7 @@ endif
 
 # Check if -pedantic option should be used
 ifeq (${DISABLE_PEDANTIC},0)
-        CFLAGS		+= 	-pedantic
+        TF_CFLAGS	+= 	-pedantic
 endif
 
 # Using the ARM Trusted Firmware BL2 implies that a BL33 image also needs to be
@@ -487,7 +487,7 @@ msg_start:
 
 # Check if deprecated declarations should be treated as error or not.
 ifeq (${ERROR_DEPRECATED},0)
-    CFLAGS		+= 	-Wno-error=deprecated-declarations
+    TF_CFLAGS		+= 	-Wno-error=deprecated-declarations
 endif
 
 # Expand build macros for the different images

make_helpers/build_macros.mk

@@ -208,11 +208,11 @@ $(eval IMAGE := IMAGE_BL$(call uppercase,$(3)))
 
 $(OBJ): $(2)
 	@echo "  CC      $$<"
-	$$(Q)$$(CC) $$(CFLAGS) -D$(IMAGE) -c $$< -o $$@
+	$$(Q)$$(CC) $$(TF_CFLAGS) $$(CFLAGS) -D$(IMAGE) -c $$< -o $$@
 
 $(PREREQUISITES): $(2) | bl$(3)_dirs
 	@echo "  DEPS    $$@"
-	$$(Q)$$(CC) $$(CFLAGS) -M -MT $(OBJ) -MF $$@ $$<
+	$$(Q)$$(CC) $$(TF_CFLAGS) $$(CFLAGS) -M -MT $(OBJ) -MF $$@ $$<
 
 ifdef IS_ANYTHING_TO_BUILD
 -include $(PREREQUISITES)
@@ -351,7 +351,7 @@ ifdef MAKE_BUILD_STRINGS
 else
 	@echo 'const char build_message[] = "Built : "$(BUILD_MESSAGE_TIMESTAMP); \
 	       const char version_string[] = "${VERSION_STRING}";' | \
-		$$(CC) $$(CFLAGS) -xc - -o $(BUILD_DIR)/build_message.o
+		$$(CC) $$(TF_CFLAGS) $$(CFLAGS) -xc - -o $(BUILD_DIR)/build_message.o
 endif
 	$$(Q)$$(LD) -o $$@ $$(LDFLAGS) -Map=$(MAPFILE) --script $(LINKERFILE) \
 					$(BUILD_DIR)/build_message.o $(OBJS)

make_helpers/windows.mk

@@ -104,6 +104,6 @@ BUILT_TIME_DATE_STRING = const char build_message[] = "Built : "${BUILD_MESSAGE_
 VERSION_STRING_MESSAGE = const char version_string[] = "${VERSION_STRING}";
 define MAKE_BUILD_STRINGS
 	@echo $$(BUILT_TIME_DATE_STRING) $$(VERSION_STRING_MESSAGE) | \
-		$$(CC) $$(CFLAGS) -x c - -o $1
+		$$(CC) $$(TF_CFLAGS) $$(CFLAGS) -x c - -o $1
 endef