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.