RFR(XS): 8169625: Libjsig build doesn't set flags for ppc64/s390 builds

[Volker Simonis]

Hi,

can I please have a review and sponsor for the following small change
which only affects ppc64/s390x but touches a shared make file:

http://cr.openjdk.java.net/~simonis/webrevs/2016/8169625/
https://bugs.openjdk.java.net/browse/JDK-8169625

It is unfortunate that the build of the libjsig library (see
make/lib/CompileLibjsig.gmk) doesn't reuse the generic compiler flags
used by the hotspot build (i.e. the ones specified in JVM_CFLAGS).
Instead, CompileLibjsig.gmk defines its own compiler  flags in
LIBJSIG_CPU_FLAGS but not for ppc64 and s390x. This leads to problems
if the compiler on these platforms uses other default settings as
configured for the OpenJDK build.

Thank you and best regards,
Volker