soong: allow overriding header files

Includes:

  Author: Jan Altensen <info@stricted.net>
  Date:   Sat Aug 7 19:41:59 2021 +0200

    soong: move header override to compiler.go

     * library.go only covers libraries

    Change-Id: I3374999d6b364dd1bbc2060996964ee7b04493e7

Change-Id: Ia9d2210605c5927b529fbe9485b0e5abd079f487