Mu IR Type checking

The Mu IR compiler currently will compile some invalid mu code, specifically I noticed the following invalid code successfully compiled (which were used in some of the tests) :

• a SHL/LSHR/ASHR instruction where the second argument is not the same as the first (in the case of the test the first argument was int<64> and the second argument was an int<8>) (this code was generated in tes_shl and test_lshr).
• passing an int<64> as an argument to a C function expecting an int<32> (this was generated by test_pass_1arg_by_stack, and test_pass_2arg_by_stack)

In addition the compiler doesn't seem to check when you use an SSA variable whether it has been assigned to yet.