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This include provides nothing useful for TF and prevents building
the fiptool using musl libc[0].

[0] https://www.musl-libc.org/



Change-Id: Ied35e16b9ea2b40213433f2a8185dddc59077884
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>

* Move stdlib header files from include/stdlib to include/lib/stdlib for
  consistency with other library headers.
* Fix checkpatch paths to continue excluding stdlib files.
* Create stdlib.mk to define the stdlib source files and include directories.
* Include stdlib.mk from the top level Makefile.
* Update stdlib header path in the fip_create Makefile.
* Update porting-guide.md with the new paths.

Change-Id: Ia92c2dc572e9efb54a783e306b5ceb2ce24d27fa