runtime: don't call funcPC from a function

runtime: don't call funcPC from a function

    The escape analysis support is not yet good enough to avoid escaping
    the argument to funcPC.  This causes unnecessary and often harmful
    memory allocation.  E.g., (*cpuProfile).addExtra can be called from a
    signal handler, and it must not allocate memory.

    Move the calls to funcPC to use variables instead.  This was done in
    the original migration to using funcPC, but was not done for newer code.

    In one case, in signal handling code, use getSigtramp.

    Reviewed-on: https://go-review.googlesource.com/92735

From-SVN: r257463