rts: Use .cfi_{start|end}proc directives
rts: Use .cfi_{start|end}proc directives

Test Plan: Validate using LLVM assembler

Reviewers: carter, erikd, simonmar

Reviewed By: simonmar

Subscribers: rwbarton, thomie

GHC Trac Issues: #15207

Differential Revision: https://phabricator.haskell.org/D4781

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc