[AsmPrinter] Make EmitLinkage and EmitVisibility public
[AsmPrinter] Make EmitLinkage and EmitVisibility public

Summary:
This allows target to implement custom emit of global variables if
required. See subsequent patch for a use case.

Change-Id: I9654197e3df24503104a54c41fff06845aed37fe

Reviewers: arsenm, kzhuravl

Subscribers: wdng, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61650

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@363519 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm