-O3 -mtune=native -march=native seems to heal problem when compiling with CLANG

[Hartmann, O.]

   Earlier last month I realized that some ports crashes on FreeBSD
   9.0-CURRENT/smd64 (most recent sources), when compiled with CLANG. In
   particular astro/stellarium and editors/leibreoffice (3.3.2) crashed.
   Those crashes where recognized on all boxes with world compiled with
   CLANG and default optimizations or -O2 -march=native. All boxes in
   question do have Core2Duo (Core2) CPUs .
   I tried now "-O3 -march=native -mtune=native" on all those boxes while
   compiling with CLANG and now the crashing software in question is now
   working correct as expected. This is strange!
   Oliver
   P.S. I have a notebook with a Core-i5 based CPU (Clarkdale). This
   notebook completely fails installing FreeBSD 9.0-CURRENT/amd64
   compiled with CLANG (I reported this). Compiling performed with the
   given defaults. I'll try to compile the OS with -O3 also and see ...