build: always use the C compiler to assemble

The ROM library is the only component in the repository that compiles
assembly files using the assembler directly. This change migrates it to
the C compiler instead, like the rest of the project.

Change-Id: I6c50660eeb9be2ca8dcb0e626c37c197466b0fa1
Signed-off-by: Chris Kay <chris.kay@arm.com>

changelog.yaml

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2021-2023, Arm Limited. All rights reserved.
+# Copyright (c) 2021-2024, Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -774,6 +774,9 @@ subsections:
       - title: PSCI
         scope: psci
 
+      - title: ROMlib
+        scope: romlib
+
       - title: GPT
         scope: gpt
 

lib/romlib/Makefile

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: BSD-3-Clause
 #
 
-AS          = $(CROSS_COMPILE)as
+AS          = $(CROSS_COMPILE)gcc
 AR          = $(CROSS_COMPILE)ar
 LD          = $(CROSS_COMPILE)ld
 OC          = $(CROSS_COMPILE)objcopy
@@ -48,11 +48,11 @@ all: $(BUILD_DIR)/romlib.bin $(LIB_DIR)/libwrappers.a
 
 %.o: %.s
 	@echo "  AS      $@"
-	$(Q)$(AS) $(ASFLAGS) -o $@ $<
+	$(Q)$(AS) -c $(ASFLAGS) -o $@ $<
 
 $(BUILD_DIR)/%.o: %.s
 	@echo "  AS      $@"
-	$(Q)$(AS) $(ASFLAGS) -o $@ $<
+	$(Q)$(AS) -c $(ASFLAGS) -o $@ $<
 
 $(BUILD_DIR)/romlib.ld: romlib.ld.S
 	@echo "  PP      $@"