Speed up make-standalone-toolchain.sh.

Instead of copying the contents of a temp directory and then deleting
the temp directory, move the contents of the temp directory.

Makes make-standalone-toolchain.sh about 6s faster (16s -> 10s).

Change-Id: Ia2db511d1554b18a31d88e90e13deb184f98f404
Merge pull request #2 from awong-dev/movedir

Speed up make-standalone-toolchain.sh.