package/llvm: bump to version 9.0.0

package/llvm: 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.

Use host-python3 to build llvm [1]

Disable explicitely Z3 support since there is no such package
in Buildroot.

[1] https://github.com/llvm-mirror/llvm/commit/213d1037e9f8b837d61eda9668112d17b0f956d0

See:
http://releases.llvm.org/9.0.0/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>