build: don't rebuild everything for libtest.la We added a -fvisibilty=default to the libtest.la CFLAGS. When automake sees that the CFLAGS are different from those of libxkbcommon.la, it figures it should recompile all of the $(libxkbcommon_la_SOURCES), instead of reusing the already-compiled object files. But actually, the convenience library is not a shared object, it's just used as an archive, thus the -fvisibility is entirely pointless. So avoid the recompilations by just removing it. Signed-off-by: Ran Benita <ran234@gmail.com>