build: build libtest.la only on 'make check'

For those just running 'make', compiling libtest is wasted heat.

Signed-off-by: Ran Benita <ran234@gmail.com>

Makefile.am

@@ -108,7 +108,7 @@ endif ENABLE_DOCS
 
 # Some tests need to use unexported symbols, so we link them against
 # a private copy of libxkbcommon with all symbols exposed.
-noinst_LTLIBRARIES = libtest.la
+check_LTLIBRARIES = libtest.la
 libtest_la_CFLAGS = $(AM_CLFLAGS) -fvisibility=default
 libtest_la_SOURCES = \
 	$(libxkbcommon_la_SOURCES) \