* config.if: If gcc_version is already set, just use it. Don't set

gcc_version_trigger if it's already set, otherwise set it to
gcc/version.c, but only if the file exists.  If it is not set and
gcc/version.c does not exist, try to extract the version number from
$CC.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@62131 138bc75d-0d04-0410-961f-82ee72b054a4