Add functionality to APInt::toString() that allows it to insert separators between groups of digits, using the C++ literal separator ' between groups. Fixes issue #58228 Reviewers: @AaronBallman, @cjdb, @tbaederr
rdar://problem/35539384 Reviewers: ahatanak, nicholas, rsmith, jkorous-apple Reviewed By: jkorous-apple Subscribers: cfe-commits, jkorous-apple Differential Revision: https://reviews.llvm.org/D42938 llvm-svn: 328671