Replace __ASSEMBLY__ with compiler-builtin __ASSEMBLER__

NOTE: __ASSEMBLY__ macro is now deprecated in favor of __ASSEMBLER__.

All common C compilers predefine a macro called __ASSEMBLER__ when
preprocessing a .S file. There is no reason for TF-A to define it's own
__ASSEMBLY__ macro for this purpose instead. To unify code with the
export headers (which use __ASSEMBLER__ to avoid one extra dependency),
let's deprecate __ASSEMBLY__ and switch the code base over to the
predefined standard.

Change-Id: Id7d0ec8cf330195da80499c68562b65cb5ab7417
Signed-off-by: Julius Werner <jwerner@chromium.org>
diff --git a/lib/romlib/Makefile b/lib/romlib/Makefile
index 60c1458..cec9404 100644
--- a/lib/romlib/Makefile
+++ b/lib/romlib/Makefile
@@ -15,7 +15,7 @@
 WRAPPER_DIR = ../../$(BUILD_PLAT)/libwrapper
 LIBS        = -lmbedtls -lfdt -lc
 INC         = $(INCLUDES:-I%=-I../../%)
-PPFLAGS     = $(INC) $(DEFINES) -P -D__ASSEMBLY__ -D__LINKER__ -MD -MP -MT $(BUILD_DIR)/romlib.ld
+PPFLAGS     = $(INC) $(DEFINES) -P -x assembler-with-cpp -D__LINKER__ -MD -MP -MT $(BUILD_DIR)/romlib.ld
 OBJS        = $(BUILD_DIR)/jmptbl.o $(BUILD_DIR)/init.o
 MAPFILE     = ../../$(BUILD_PLAT)/romlib/romlib.map