package/clang: bump to version 9.0.0

package/clang: bump to version 9.0.0

The github download url doesn't contain the llvm 9.0.0 archive,
so use the previous url.

Since v9.0.0, it was relicensed to the Apache License 2.0 with
LLVM Exceptions. Update the license file hash.

See:
http://releases.llvm.org/9.0.0/tools/clang/docs/ReleaseNotes.html

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: Valentin Korenblit <valentinkorenblit@gmail.com>
Cc: Joseph Kogut <joseph.kogut@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>