Makefile: Revise utsname and clock_gettime test

Clean up the feature target by outsourcing the test to an own variable.
Change the print output and don't write to the build-details file.
HAS_CLOCK_GETTIME=no replaces DISABLE_CLOCK_GETTIME=yes

This is in preparation for further changes.

Change-Id: Ie1f43b3d5a8ad79bff3f9bbc21f359ec35abc42a
Signed-off-by: Thomas Heijligen <thomas.heijligen@secunet.com>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/58618
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

Makefile.d/clock_gettime_test.c

@@ -0,0 +1,9 @@
+#include <time.h>
+int main(int argc, char **argv)
+{
+	(void)argc;
+	(void)argv;
+	struct timespec res;
+	clock_gettime(CLOCK_REALTIME, &res);
+	return 0;
+}