libpayload: Start using only internal and compiler headers.

When building other payloads with lpgcc the -nostdinc flag was injected into
CFLAGS, but when building libpayload itself some headers were being used from
the host system. This change puts -nostdinc into the Makefile and xcompile
script, fixes up one include path in include/inttypes.h, adds the compiler
provided include directory to the include search path, and deletes the two now
redundant stdint.h files.

BUG=None
TEST=With this and other changes, built libpayload and depthcharge for Daisy,
Link, and Fox.
BRANCH=None

Change-Id: Ia7817fceab5297cd82ccc0d392330de0df61980e
Signed-off-by: Gabe Black <gabeblack@google.com>
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/2710
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

payloads/libpayload/util/xcompile/xcompile

@@ -41,7 +41,7 @@ testcc() {
 	local tmp_o="$TMPFILE.o"
 	rm -f "$tmp_c" "$tmp_o"
 	echo "_start(void) {}" >"$tmp_c"
-	"$1" -nostdlib -Werror $2 "$tmp_c" -o "$tmp_o" >/dev/null 2>&1
+	"$1" -nostdinc -nostdlib -Werror $2 "$tmp_c" -o "$tmp_o" >/dev/null 2>&1
 }
 
 testas() {