Merge pull request #2596 from MartinNowak/metastrings

readd std.metastrings as deprecated module
Conflicts:
	posix.mak
	win32.mak
	win64.mak
Merge pull request #2610 from MartinNowak/2.066

Cherry-picks for 2.066.1
std.math: use most inline x86/x64 assembly only if real is defined as 80-bit x87
std.math: use more LLVM intrinsics if available
Merge pull request #3 from kinke/math

std.math: use most inline x86/x64 assembly only if real is defined as x87
Fix non-Win64 version.

You can't use `static if` to conditionally define a version identifier.
Use __traits(compiles, llvm_<...>) instead of version identifiers.
std.math: Remove usage of intrinsic llvm.exp

This causes a unit test failure.
std.math: Remove usage of intrinsic llvm.pow.

This causes a unit test failure.
std.math: Remove usage of intrinsic llvm.exp2.

This causes a unit test failure.
Fix mingw version of std.stdio.

Some constants and the prototype for _fdopen were missing.
Merge tag 'v2.066.1' into ldc