TestPosixSig explicitly checks for warning messages from the signal checker.

For static-jdk, libjsig is currently statically linked with bin/java. When running on static JDK, during VM initialization 'install_signal_handlers' determines libjsig is already loaded since 'JVM_begin_signal_setting' lookup is successful. Based on that, it disables the periodic signal checker after installing VM signal handlers. 'os::run_periodic_checks' (signal checker) always returns immediately without doing any checks, and there is no warning messages from the checker when signal handler is modified.