Add callWithStackShell() for Linux/PPC32.

The implementation was only available as a separate patch.
Fix a bug passing the exception object.

A pointer to the exception object seems to be expected here.
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Remove ldc.longdouble as it conflicts with MSVCRT 2013+ and is obsolete if real == double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