fix: Allow disabling some abi compat tests

fix: Allow disabling some abi compat tests

Allow disabling ABI compat tests that rely on a library using a symbol from
the global offset table even if it provides its own copy, which is the
default behavior on Linux.

This situation happens when using the '-Bsymbolic-functions' linker flag
which binds references to public symbols in a library to the definition
within the library, bypassing the global offset table.

To disable those tests when running the test suite, set the
UST_TESTS_LD_SYMBOLIC_FUNC environment variable to any value, for
example :

  make check UST_TESTS_LD_SYMBOLIC_FUNC=1

Change-Id: I1ed23d90bbe1b174ab7b4fccfb40b701b291c074
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>