[android] Provide correct temporary directory path.
[android] Provide correct temporary directory path.

Android Bionic uses /data/local/tmp as the temporary writable directory.
TMPDIR is rarely set and /tmp doesn't exist.

There's some usage of /tmp/ in the tests that might be wrong and might
need to be fixed in the future, but I have to check one by one and right
now I don't have a device to test on.

parkera/swift-corelibs-foundation,parkera/swift-corelibs-foundation,parkera/swift-corelibs-foundation,parkera/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,parkera/swift-corelibs-foundation,e78l/swift-corelibs-foundation,e78l/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation