lib: add string.c to verstage

Change-Id: I5aa3bb2c72dcf127d418c989f6b63c9b1f412f08
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34557
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/lib/Makefile.inc

@@ -57,6 +57,7 @@ verstage-y += halt.c
 verstage-y += fmap.c
 verstage-y += libgcc.c
 verstage-y += memcmp.c
+verstage-y += string.c
 verstage-$(CONFIG_COLLECT_TIMESTAMPS) += timestamp.c
 verstage-y += boot_device.c
 verstage-$(CONFIG_CONSOLE_CBMEM) += cbmem_console.c