Fix the build on alpha by removing -ffast-math from the build cflags.
 Remove an unnecessary configure script from when this was built from
 Register conflicts for dri-devel in dri.
Submitted by:  krismail
 Try to respect PTHREAD_LIBS, to unbreak the build on 4.x.
 Respect CXXFLAGS a little more thoroughly.
PR:  ports/75473
Submitted by:  KIMURA Yasuhiro, yasu at utahime dot org, among many others
Based on:  patch by thierry