glx: build tests after libglx.la

Previously, if you ran make followed by make check it would work, but
if you just ran make check the test program would fail to compile.

Reviewed-by: Jon TURNEY <jon.turney@dronecode.org.uk>

src/glx/Makefile.am

@@ -24,7 +24,7 @@ SHARED_GLAPI_CFLAGS = -DGLX_SHARED_GLAPI
 SHARED_GLAPI_LIBS = $(top_builddir)/src/mapi/shared-glapi/libglapi.la
 endif
 
-SUBDIRS=tests
+SUBDIRS=. tests
 
 GLAPI_LIB = ../mapi/glapi/libglapi.la