Add Makefile target (check-nolink) to compile all source without linking
Note: it is assumed --enable-shared is not passed to configure.
* Makefile.am (check-nolink-local): New Makefile phony target (just
redirects to "all").
* configure.ac: Define check-nolink by AM_EXTRA_RECURSIVE_TARGETS.
* tests/Makefile.am (TEST_OBJS): New variable (with a list of the test
.o files).
* tests/Makefile.am (check-nolink-local): New Makefile phony target
(forces all tests to be compiled but not linked).