tests: Add lib/libgcc-test test case

Add tests for src/lib/libgcc.c __clzsi2() implementation. Unlike GCC
implementation, coreboot one can handle zero input.

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: I3f46071d0921e8c5edc5df3c296d11c77de01c88
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56257
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
diff --git a/tests/lib/Makefile.inc b/tests/lib/Makefile.inc
index 6750353..028db73 100644
--- a/tests/lib/Makefile.inc
+++ b/tests/lib/Makefile.inc
@@ -31,6 +31,7 @@
 tests-y += spd_cache-ddr3-test
 tests-y += spd_cache-ddr4-test
 tests-y += cbmem_stage_cache-test
+tests-y += libgcc-test
 
 string-test-srcs += tests/lib/string-test.c
 string-test-srcs += src/lib/string.c
@@ -177,3 +178,5 @@
 cbmem_stage_cache-test-cflags += -I 3rdparty/vboot/firmware/include
 cbmem_stage_cache-test-cflags += -I $(src)/commonlib/include
 cbmem_stage_cache-test-config += CONFIG_CBMEM_STAGE_CACHE=1
+
+libgcc-test-srcs += tests/lib/libgcc-test.c