The conversion was done with an automated tool and then
modified only as necessary to make it compile and run.
[This CL is part of the removal of C code from package runtime.
See golang.org/s/dev.cc for an overview.]
LGTM=r
R=r
CC=austin, dvyukov, golang-codereviews, iant, khr
https://golang.org/cl/167540043
semacquire might need to park the currently running G. It can
only park if called from the G stack (because it has no way of
saving the M stack state). So all calls to semacquire must come
from the G stack.
The three violators are GOMAXPROCS, ReadMemStats, and WriteHeapDump.
This change moves the semacquire call earlier, out of their C code
and into their Go code.
This seldom caused bugs because semacquire seldom actually had
to park the caller. But it did happen intermittently.
Fixes#8749
LGTM=dvyukov
R=golang-codereviews, dvyukov, bradfitz
CC=golang-codereviews
https://golang.org/cl/144940043
