The financial cost of the network I/O for the Clang install artifacts is
quite significant. afd3478f37c8 improved this by creating tarballs. This
commit improves the tarball by using xz compression instead of gzip. This
option is the slowest, but gives the smallest size.
size time time
(compression) (decompression)
gzip 51 M 7 s 1.2 s
bz2 44 M 17 s 5.8 s
xz 33 M 76 s 3.1 s
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D150062
f271df0e79