scons: Pass -Qunused-arguments to clang to skip warnings about unused -I paths

Step 1/2 in making it possible to build in strict mode with clang 3.3
and scons here.
scons: Pass -Wno-parentheses-equality to clang for src/lua/ library objects

Step 2/2 in making it possible to build in strict mode with clang 3.3
and scons here.