build(cert-create): don't generate `build_msg.c`

This change avoids generating a build message source file on the shell,
instead using the `__DATE__` and `__TIME__` macros directly.

Change-Id: Ieda75bbac174847c716701bce8dd10b8e9975902
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/tools/cert_create/Makefile b/tools/cert_create/Makefile
index 7670939..16f4aa3 100644
--- a/tools/cert_create/Makefile
+++ b/tools/cert_create/Makefile
@@ -18,6 +18,7 @@
 include ${MAKE_HELPERS_DIRECTORY}common.mk
 include ${MAKE_HELPERS_DIRECTORY}defaults.mk
 include ${MAKE_HELPERS_DIRECTORY}toolchain.mk
+include ${MAKE_HELPERS_DIRECTORY}utilities.mk
 
 ifneq (${PLAT},none)
 TF_PLATFORM_ROOT	:=	../../plat/
@@ -60,7 +61,7 @@
   HOSTCCFLAGS += -O2 -DLOG_LEVEL=20
 endif
 
-HOSTCCFLAGS += ${DEFINES}
+HOSTCCFLAGS += ${DEFINES} -DPLAT_MSG=$(call escape-shell,"$(PLAT_MSG)")
 # USING_OPENSSL3 flag will be added to the HOSTCCFLAGS variable with the proper
 # computed value.
 HOSTCCFLAGS += -DUSING_OPENSSL3=$(USING_OPENSSL3)
@@ -84,10 +85,7 @@
 
 ${BINARY}: ${OBJECTS} Makefile
 	$(s)echo "  HOSTLD  $@"
-	$(q)echo 'const char build_msg[] = "Built : "__TIME__", "__DATE__; \
-                const char platform_msg[] = "${PLAT_MSG}";' | \
-                $(host-cc) -c ${HOSTCCFLAGS} -xc - -o src/build_msg.o
-	$(q)$(host-cc) src/build_msg.o ${OBJECTS} ${LIB_DIR} ${LIB} -o $@
+	$(q)$(host-cc) ${OBJECTS} ${LIB_DIR} ${LIB} -o $@
 
 %.o: %.c
 	$(s)echo "  HOSTCC  $<"
@@ -99,7 +97,7 @@
 endif
 
 clean:
-	$(call SHELL_DELETE_ALL, src/build_msg.o ${OBJECTS})
+	$(call SHELL_DELETE_ALL,${OBJECTS})
 
 realclean: clean
 	$(call SHELL_DELETE,${BINARY})
diff --git a/tools/cert_create/src/main.c b/tools/cert_create/src/main.c
index 14610ed..edc2d68 100644
--- a/tools/cert_create/src/main.c
+++ b/tools/cert_create/src/main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2022, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2024, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -66,10 +66,8 @@
 static int save_keys;
 static int print_cert;
 
-/* Info messages created in the Makefile */
-extern const char build_msg[];
-extern const char platform_msg[];
-
+static const char build_msg[] = "Built : " __TIME__ ", " __DATE__;
+static const char platform_msg[] = PLAT_MSG;
 
 static char *strdup(const char *str)
 {