helper functions for building generic binary

to compile a generic extempore:

EXT_LLVM_DIR=<llvm-dir> EXT_BUILD_GENERIC=1 ./all.bash

to compile a generic stdlib:

EXT_LLVM_DIR=<llvm-dir> EXT_BUILD_GENERIC=1 ./extempore --run libs/create-stdlib.xtm
Merge branch 'master' of github.com:digego/extempore

* 'master' of github.com:digego/extempore:
  couple of small lib changes
  example file cleanup
  move preload check after other loads
  unrolled shader loop
  framebuffer check for some drivers