RFR (S) 8134537: Much nearly duplicated code for sun.misc.Signal support

[coleen.phillimore at oracle.com]

Summary: merged jvm_<os>.cpp into jvm_posix.cpp mostly

See bug for more info.  The os_<os>.cpp code is sort of duplicated but 
different enough to not be worth refactoring, for this feature.  I was 
in the area, so merged this one part.

Tested with hs-tier1,2 runtime/signal tests and 
sun/misc/SunMiscSignalTest.java.

open webrev at http://cr.openjdk.java.net/~coleenp/8134537.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8134537

Thanks,
Coleen