[CMake] Set Policy CMP0048 to NEW

CMake 3.0 introduced the VERSION option for the project() command. If you don't specify the VERSION in the function it will clear out variables matching ${PROJECT_NAME}_VERSION_${MAJOR|MINOR|PATCH|TWEAK}.

This makes overriding LLVM_VERSION_* not work properly with newer versions of CMake. To make this work properly we need to:

(1) Optionally set the policy to NEW
(2) Move default versions and setting PACKAGE_VERSION to before the call to project()
(3) If the policy is set, pass the VERSION and LANGUAGES options in the new format

This change should have no behavioral change for CMake versions before 3.0, and it makes the behavior of later versions match the earlier versions.

llvm-svn: 250275