a common source of oddities and, in theory, removes some redundant ABI
computations.  Also fixes a miscompile I introduced yesterday by refactoring
some code and causing a slightly different code path to be taken that
didn't perform *parameter* type canonicalization, just normal type
canonicalization;  this in turn caused a bit of ABI code to misfire because
it was looking for 'double' or 'float' but received 'const float'.

llvm-svn: 97030