PR go/90110

	PR go/90110
    compiler: use temporary to avoid early destruction

    The code was passing a substr directly to strtol, and then checking
    the *end value returned by strtol.  But the substr could be destroyed
    as soon as strtol returns, making the test of *end invalid.

    Also fix an incorrect test of the string index rather than the value.

    Fixes https://gcc.gnu.org/PR90110

    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/172663

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@270434 138bc75d-0d04-0410-961f-82ee72b054a4