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.
1. Main include corresponding to .cpp file, if any.
2. DMD and LDC includes.
3. LLVM includes.
4. System includes.
Also updated a few include guards to match the default format.
On x86_64, a proper solution (see GitHub #120) is still needed,
but this will have to wait until the special case for extern(D)
is gone from the implementation.
We need this right now as std.digest.md in 2.061 triggers a
miscompilation issue in the LLVM x86 backend (not the optimizer!)
when returning them directly as LLVM arrays.
The solution is to replace Attribute with AttrBuilder in IrFuncTyArg.
Then the argument attributes can be easily manipulated and transformed
into the final AttributeSet.
