tests: use 'check_PROGRAMS' instead of 'noinst_PROGRAMS'

When using 'check_PROGRAMS', autoconf/automake generates smarter
Makefiles, so that the test programs are not being compiled during
the normal 'make all', but only during 'make check'.

Change-Id: I8118ee3d3da9bdcd0c691471ef91b95dba21004a
diff --git a/tests/slhc/Makefile.am b/tests/slhc/Makefile.am
index b6738c2..0167f44 100644
--- a/tests/slhc/Makefile.am
+++ b/tests/slhc/Makefile.am
@@ -3,7 +3,7 @@
 
 EXTRA_DIST = slhc_test.ok
 
-noinst_PROGRAMS = slhc_test
+check_PROGRAMS = slhc_test
 
 slhc_test_SOURCES = slhc_test.c