Fix GCC message style conformance for macros

Same as fc5f1448, but fix it for the fail_msg() and
expect_assert_failure() macros in cmocka.h.
src: Remove unneeded #ifdef for HP-UX

Commit c5ac6b5 fixed a char* to int conversion truncation warning on
64-bit HP-UX by #ifdef'ing out this:
    assert_false("BUG: shouldn't be here!");
But, commit c5ac6b5 fixed the warning for all 64-bit platforms by
replacing assert_false() with assert_null(). Therefore, the #ifdef for
HP-UX is no longer needed.

Signed-off-by: Chad Versace <chad@chad-verssace.us>
src: Fix return value of _run_tests()

The Doxygen claims that _run_tests() returns 1 on failure. However, the
code returns the total number failures, or -1 under more significant
error conditions.

Make the code match the docs. Return 1 on failure.

Signed-off-by: Chad Versace <chad@chad-verssace.us>
wip: Define enum TestResult
wip! src: Add test_result param to exit_test()
src: Use TestResult in run_test(), _run_tests()
wip! TEST_SKIP