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/include/common/bl_common.h b/include/common/bl_common.h
index 4c8a17c..647ae85 100644
--- a/include/common/bl_common.h
+++ b/include/common/bl_common.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2022, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2024, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -180,8 +180,6 @@
 void dyn_disable_auth(void);
 #endif
 
-extern const char build_message[];
-extern const char version_string[];
 const char *get_version(void);
 
 void print_entry_point_info(const entry_point_info_t *ep_info);
diff --git a/include/common/build_message.h b/include/common/build_message.h
new file mode 100644
index 0000000..b7c2f72
--- /dev/null
+++ b/include/common/build_message.h
@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2024, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef BUILD_MESSAGE_H
+#define BUILD_MESSAGE_H
+
+static const char build_message[] = "Built : " BUILD_MESSAGE_TIMESTAMP;
+static const char build_version_string[] = BUILD_MESSAGE_VERSION_STRING;
+static const char build_version[] = BUILD_MESSAGE_VERSION;
+
+#endif /* BUILD_MESSAGE_H */