Create a library file for libc

TF Makefile was linking all the objects files generated for the
c library instead of creating a static library that could be
used in the linking stage.

Change-Id: I721daea097e9b13cbb42c9f8eaa2af8fea0799cf
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/lib/libc/libc.mk b/lib/libc/libc.mk
new file mode 100644
index 0000000..ded3d74
--- /dev/null
+++ b/lib/libc/libc.mk
@@ -0,0 +1,25 @@
+#
+# Copyright (c) 2016-2017, ARM Limited and Contributors. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+LIBC_SRCS	:=	$(addprefix lib/libc/,	\
+			abort.c				\
+			assert.c			\
+			exit.c				\
+			mem.c				\
+			printf.c			\
+			putchar.c			\
+			puts.c				\
+			sscanf.c			\
+			strchr.c			\
+			strcmp.c			\
+			strlen.c			\
+			strncmp.c			\
+			strnlen.c			\
+			subr_prf.c			\
+			timingsafe_bcmp.c)
+
+INCLUDES	+=	-Iinclude/lib/libc		\
+			-Iinclude/lib/libc/sys