Add new exp2, log10, log2 LLVM 3.3 intrinsics to ldc.intrinsics...

and uses them in core.math. Highlight some core.math Windows bugs
related to MSVCRT's incomplete C99 implementation.

Patch provided by kinke. Thank you!
Merge branch 'ldc' into ldc-merge-2.061
fix struct literal rvalue change
Merge pull request #7 from pinver/ldc

fix struct literal rvalue change
Merge branch 'ldc' into ldc-merge-2.061
Disable the ldc.longdouble module since it is incompatible with the new core.stdc.math module which already implements the long double versions of all functions supported by MSVCRT. I think all efforts to implement some missing C99 functions should go into Phobos' std.math, since that module already contains some core.stdc.math-independent implementations (primarily in assembler).
Reworked core.stdc.math and core.stdc.tgmath for MSVCRT support
Improved MSVCRT support in core.stdc.stdlib
Improved MSVCRT support in core.stdc.stdio module.
Use MSVCRT version in core.stdc.wchar_; embed comment to remove code after Phobos pull.
Cosmetic fixes: move version declarations after imports.