tests: Add <tests/test.h> wrapper header and fix --gc-sections

<cmocka.h> requires a few standard headers to be explicitly included
before itself or it will throw compilation errors. Having to always
include these headers in the right order in every test is cumbersome.
Instead, this patch encapsulates the problem in a new <tests/test.h>
header that all tests should include (instead of <cmocka.h> directly).

Also fix --gc-sections in the test framework which needs to be passed
for linking, not for compiling.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: I4284d74c8673708e21a5266eb42f7b9ae19a1b12
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41045
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jan Dabros
Reviewed-by: Paul Fagerburg <pfagerburg@chromium.org>

tests/include/tests/test.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* This file is part of the coreboot project. */
+
+#ifndef _TESTS_TEST_H
+#define _TESTS_TEST_H
+
+/*
+ * Standard test header that should be included in all tests. For now it just encapsulates the
+ * include dependencies for Cmocka. Test-specific APIs that are so generic we would want them
+ * available everywhere could also be added here.
+ */
+
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+
+#endif /* _TESTS_TEST_H */