Added sage-opt to run LLVM's opt with SAGE

SAGE's shell sets a bunch of environmental variables which are necessary
for using SAGE's Python libraries. sage-opt is used run opt with these
variables set.
Added scripts to execute stuff with SAGE's shell

SAGE's sh shell sets a bunch of environmental variables. We should run
LLVM's opt, CC and CXX with these variables set. The following commits
will fix this.
Changed llvm-python to work with SAGE's sh.
Changed/added makefiles to work with SAGE's sh