Use the existing build configuration parameter ENABLE_BACKTRACE to compile out all pretty stack trace support when backtraces are disabled.
Use the existing build configuration parameter ENABLE_BACKTRACE to compile out all pretty stack trace support when backtraces are disabled.

This has the nice secondary effect of allowing LLVM to continue to build
for targets without __thread or thread_local support to continue to work
so long as they build without support for backtraces.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@227423 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,dslab-epfl/asap,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,dslab-epfl/asap,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm