Since commit 5990ecb741 (Compute implicit include directories from
compiler output, 2018-12-07) we now have compiler implicit include
directory computation for gcc and clang. It should be safe now to pass
these to `moc`. This patch re-enables passing the compiler implicit
include directories to `moc`, which was disabled due to issue #18669.
Fixes: #18041
Issue: #18669
Sebastian Holtermann
03dbb62d31