Log Message:
gcc{48,49,5,6,7,8}: In the case of a "system GCC", detect if the system
libgcc is newer than the one about to be installed. If so, don't install
the libgcc.

Having an older libgcc appear in the lookup may result in binaries not
running, as they need symbols from the newer libgcc.
Such a case is PR pkg/54506.

Leaves SunOS unchanged, by request from jperkin.