RFR JDK-8022407 sun/misc/CopyMemory.java fails with SIGSEGV in Unsafe_SetByte+0x35

[Lois Foltan]

Please review the following fix:
     open webrev at http://cr.openjdk.java.net/~hseigel/bug_jdk8022407/

Bug:
     bug link at https://bugs.openjdk.java.net/browse/JDK-8022407

Summary of fix:

The JDK 8 build on MacOS, when built with the Xcode 4.6.2 clang++ 
compiler, exhibited a compiler optimization issue when prims/unsafe.cpp 
was compiled at the default -Os level. As a work around fix, knock the 
optimization level down down to -O0.

Tests:
     MacOS: built fastdebug & product images using clang++ (ran JTREG & 
vm.quick.testlist)
                    built using llvm-g++ to verify prims/unsafe.cpp 
remained compiled at -Os

Thank you,
Lois