These are the runtime support functions for letting Go code interoperate
with the C/C++ memory sanitizer.  Calls to msanread/msanwrite are now
inserted by the compiler with the -msan option.  Calls to
msanmalloc/msanfree will be from other runtime functions in a subsequent
CL.

Change-Id: I64fb061b38cc6519153face242eccd291c07d1f2
Reviewed-on: https://go-review.googlesource.com/16162
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>