r175132 - Partially revert r175117 so that we don't break assumptions about how

[Tim Northover]

> What are the other deviations from language linkage that you know? The
> one I know in that we don't include it in function types. Do you know
> the rationale for it being what it is on the standard?

While it's mostly a matter of pragmatism rather than principle, ARM's
C Language Extension document (ACLE) defines
__atrribute__((pcs("aapcs"))) and the hardfloat equivalent as
language-linkage modifiers.

The entire purpose of that distinction is calling conventions, and we
make use of the fact that the resulting types are different.

Tim.