Add 'pure nothrow' to __asm statement.

This allows the __asm statement to be used in pure and/or nothrow
functions like the D inline assembler statement.
Add more math functions for Windows.

The set of required functions is now complete. Most functions are
also implemented and work for Win32 and Win64.
Remove pragma(LDC_allow_inline) because __asm can be inlined by default.
Fixed 2.062 OS X regression introduced by 830e0770.

This reverts the module to the pre-830e0770 state for
non-Linux. It should probably be amended to follow the
same conventions as for other module files, which might
help to avoid such problems.

This is a back-port of druntime pull request #479.
Intrinsics from LLVM 3.3 are also available in LLVM 3.4.
Intrinsics from LLVM 3.3 are also available in LLVM 3.4.
Backported sane callWithStackShell implementation; added ARM support.