fixed an issue where the configured c compiler was ignored. also removed a flag that is incompatible with clang

git-svn-id: https://smlnj-gforge.cs.uchicago.edu/svn/manticore/trunk@5696 ac4fbcad-d21d-0410-b760-c7b1d3380187
fix for previous commit, was allowing extra flags

git-svn-id: https://smlnj-gforge.cs.uchicago.edu/svn/manticore/trunk@5697 ac4fbcad-d21d-0410-b760-c7b1d3380187