Mostly revert r330672.
Mostly revert r330672.

The test is apparently needed e.g. for check-cfi on Windows where we get
  'C:/b/slave/sanitizer-windows/build/./bin/clang.exe': command not found
without it.  Try to fix the problem that was fixed by r330672 by also checking
for isabs() instead.



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@330673 91177308-0d34-0410-b5e6-96231b3b80d8

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