We're not supposed to be redefining PACKAGE_VERSION, PACKAGE_...
from the configure generated confdefs.h. This patch rudely adds
paper over the problem. The compiler warnings are a problem for
us since our checking of various compiler flags assumes that
no news is good news, and that any warning messages are due
to the flags under test. The regression appears when using
an autoconf >= 2.64, at least, but not with 2.61.
The same issue appears in the pthread test because our conftest
unconditionally #defines _GNU_SOURCE, but autoconf ends up doing
that in the confdefs.h.
Avoid calling libtool to link every single test case, by building just one
binary from all the sources.
This binary is then given the task of choosing tests to run (based on user
selection and individual test requirement), forking each test into its own
process and accumulating the results.
