runtime·main·f is normalized by the linker to runtime.main.f, as is
the compiler-generated symbol runtime.main·f.  Change the former to
runtime·mainPC instead.

Fixes issue #9934

Change-Id: I656a6fa6422d45385fa2cc55bd036c6affa1abfe
Reviewed-on: https://go-review.googlesource.com/8234
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>