Integrate obj_includelib into its only caller.
Move calling convention conversion into TargetABI.

The code is tightly coupled to TargetABI (the transformations
there only make sense knowing that the right CC is selected).
MinGW: pragma(lib,...) DMD compatibility hacks.
Fold in d_do_test Windows fixes.
Fix ABI on Win32.

We can't simply use the C calling convention, as the D(MD)
ABI is callee-pop, and this is hardcoded in naked functions
with stack parameters.

The \1 "trick" is normally used to avoid prefixes added by
LLVM; on the 3.2 release, a patch is needed to make it work
for the @<n> stdcall suffixes as well.
MinGW: Use __mingw_strtold instead of strtold.

The latter fails to parse hex floating point literals.
MinGW runtime and test suite updates.