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/bl2u/bl2u_main.c b/bl2u/bl2u_main.c
index fcb73b9..cd13def 100644
--- a/bl2u/bl2u_main.c
+++ b/bl2u/bl2u_main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2020, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2024, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -14,6 +14,7 @@
 #include <bl1/bl1.h>
 #include <bl2u/bl2u.h>
 #include <common/bl_common.h>
+#include <common/build_message.h>
 #include <common/debug.h>
 #include <drivers/auth/auth_mod.h>
 #include <drivers/console.h>
@@ -27,7 +28,7 @@
  ******************************************************************************/
 void bl2u_main(void)
 {
-	NOTICE("BL2U: %s\n", version_string);
+	NOTICE("BL2U: %s\n", build_version_string);
 	NOTICE("BL2U: %s\n", build_message);
 
 #if SCP_BL2U_BASE