[SV 40240] Use configure info to build load test shared libs

[SV 40240] Use configure info to build load test shared libs

* tests/config-flags.pm.in: A new file containing variable assignments
for the test suite; these variables are set by configure to contain
the values detected there for compilers, flags, etc.
* tests/run_make_tests.pl: Require the config-flags.pm file
* tests/scripts/features/load, tests/scripts/features/loadapi: Use the
configure-provided values when building the shared test library.
* configure.ac: Replace tests/config-flags.pm.in
* Makefile.am: Make sure tests/config-flags.pm is up to date