Replaced git:// link with https:// which gets through firewalls easier.

Replaced archive with .xz. The one currently in the mirrors has the wrong
hash. .xz is also smaller than .gz.

Eliminated already default CMake option.

Eliminated Build/InstallDev with CMAKE_INSTALL.

Added PKG_BUILD_PARALLEL for faster compilation.

Signed-off-by: Rosen Penev <rosenp@gmail.com>