This moves platform-independent SunPro compiler flags into separate
"Compiler/SunPro-<lang>.cmake" modules. Platform-specific flags are
left untouched.
This teaches Modules/Platform/Linux-SunPro-CXX.cmake the -rpath-link flag. The
SunPro C++ compiler does not have a '-Wl,' option, so we just pass the flag
directly.
This problem was exposed by the ExportImport test now that it links an
executable through the C++ compiler with the -rpath-link flag.