<rdar://problem/13477190> On Darwin, use DARWIN_USER_TEMP_DIR or DARWIN_USER_CACHE_DIR for the system temporary directory.

The DARWIN_USER_TEMP_DIR and DARWIN_USER_CACHE_DIR configuration
settings are more idiomatic for Darwin than the TMPDIR environment
variable.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177669 91177308-0d34-0410-b5e6-96231b3b80d8