main/mesa: rebuild against llvm-3.6.1

The commit 08fdc970 (main/llvm: update to 3.6.1) moved from
autotools/configure to cmake build. The cmake build no longer builds
libLLVM-<version>.so which was used by mesa. Instead it builds more
granular libs. So we need to rebuild mesa.

see also https://llvm.org/bugs/show_bug.cgi?id=15493