clang as system compiler and cpp is clang cpp (as opposed to GNU cpp).
This is done by removing the configure test for cpp completely. Using
clang cpp will make some manual pages as well as some scripts get slightly
wierd whitespace formatting. However, it does not affect the function of
the scripts or the instructions in the manual pages.
PR: ports/166373
Submitted by: Jakub Lach <jakub_lach@mailplus.pl> (PR)
Patch by: me (with ideas from PR and mailing list)
Tested by: Jakub Lach <jakub_lach@mailplus.pl>, me
Approved by: kwm (mentor)
Obtained from: xorg staging area
