libstdc++ testsuite failure on AIX

[David Edelsohn]

	With help from Ian Lance Taylor on IRC, the problem appears to be
due to the change from building testsuite_abi.cc with Make to building it
in DejaGNU.  Make cared about the exit code, but DejaGNU fails if any
unexpected output is produced.  On AIX, building testsuite_abi.cc produces
an expected warning:

/farm/dje/src/src/libstdc++-v3/testsuite/testsuite_abi.cc:1: warning: -ffunction-sections may affect debugging on some targets

Daniel Jacobowitz suggests adding "-w" to the options, which does suppress
the warning when tested manually.

David