Add a warning when there is a macro defintion that has named parameters but
the body does not use them and it appears the body has positional parameters.

This can cause unexpected results as in the added test case.  As the darwin
version of gas(1) which only supported positional parameters, happened to
ignore the named parameters.  Now that we want to support both styles of
macros we issue a warning in this specific case.

rdar://12861644