core.stdc.math: full support for MSVCRT 2013+
Remove ldc.longdouble as it conflicts with MSVCRT 2013+ and is obsolete if real == double
core.stdc.fenv: get rid of linking error when using MSVC 2013+
core.math: proper support for MSVCRT 2013+
core.math: use LLVM fabs intrinsic
Merge pull request #13 from kinke/ldcmath

core.stdc.math: full support for MSVCRT 2013+