Add a facility to skip running some test suites

With the build option SKIP_TEST_SUITES=..., the specified test suites
are built, but skipped when running tests. Usage:
    make check SKIP_TEST_SUITES=timing,gcm
or
    cmake -D SKIP_TEST_SUITES=timing,gcm ...

The list can be separated by any of space, comma or semicolon, and each
element can be a regular expression in ERE syntax except that "." stands
for itself. Skipping "foo" skips not only "foo" itself but also
any "foo.bar", but does not skip "foobar".
diff --git a/tests/Makefile b/tests/Makefile
index d85617f..03f1a7f 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -444,7 +444,8 @@
 	del /Q /F *.c *.exe
 endif
 
+# Test suites caught by SKIP_TEST_SUITES are built but not executed.
 check: $(APPS)
-	perl scripts/run-test-suites.pl
+	perl scripts/run-test-suites.pl --skip=$(SKIP_TEST_SUITES)
 
 test: check