[MC] Pass the symbol rather than its name to onSymbolStart()
Summary: This allows targets to also consider the symbol's type and/or address if needed.
Reviewers: scott.linder, jhenderson, MaskRay, aardappel
Reviewed By: scott.linder, MaskRay
Subscribers: dschuff, sbc100, jgravelle-google, hiraditya, aheejin, rupprecht, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D82090