compiler: permit inlining variable declaration statements

This adds all of two inlinable functions to the standard library:
crypto/subtle.ConstantTimeLessOrEq, regexp.(*Regexp).Copy.

Change-Id: Iefa88383f344cb6f463f04dfcadf473c5844ae60
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/176378
Reviewed-by: Than McIntosh <thanm@google.com>
3 files changed