Don't modify user vars because they will get passed down (modified) to sub-makes and recursively append causing huge command lines and incorrect compilation results.
Don't modify user vars because they will get passed down (modified) to
sub-makes and recursively append causing huge command lines and incorrect
compilation results.

Also, fix the printvars target to align its output and ensure that the
contents of variables can't get interpreted by the shell.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@17348 91177308-0d34-0410-b5e6-96231b3b80d8

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