build: remove `MAKE_BUILD_STRINGS` function

This function causes the build message to be generated and compiled in
two different ways, with one way done inside `build_macros.mk` and the
other done inside `windows.mk`, mostly because it's done by generating
the C file on the command line.

We can instead replace this whole build message generation sequence with
a simple standard C compilation command and a normal C file.

Change-Id: I8bc136380c9585ddeec9a11154ee39ef70526f81
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/bl31/bl31_main.c b/bl31/bl31_main.c
index 9807817..cae9b14 100644
--- a/bl31/bl31_main.c
+++ b/bl31/bl31_main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2023, Arm Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2024, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -13,6 +13,7 @@
 #include <bl31/bl31.h>
 #include <bl31/ehf.h>
 #include <common/bl_common.h>
+#include <common/build_message.h>
 #include <common/debug.h>
 #include <common/feat_detect.h>
 #include <common/runtime_svc.h>
@@ -128,7 +129,7 @@
 	/* Init per-world context registers for non-secure world */
 	manage_extensions_nonsecure_per_world();
 
-	NOTICE("BL31: %s\n", version_string);
+	NOTICE("BL31: %s\n", build_version_string);
 	NOTICE("BL31: %s\n", build_message);
 
 #if FEATURE_DETECTION