Fix for 8072147 breaks JDK 9 build with older gcc on Mac.

The above bug was fixed in JDK 9 on this thread :-
http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2015-June/015282.html

when it came to the JDK8 backport it was implemented differently since gcc did not
support the thread local storage in the older gcc
http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2015-July/015309.html

This means that those of us who are stuck with the older gcc because we need to
build several releases can no longer build on JDK 9.

~/jdk9/hotspot/src/os/bsd/vm/jsig.c:45: error: thread-local storage not supported for this target
make[10]: *** [libjsig.dylib] Error 1

Whilst there is an official JDK 9 compiler for each platform we should endeavour
to allow building on as many versions as possible. The JDK 8 solution should be
foward ported to JDK 9 asap.