Update to current libcxxabi for new exception code.
Update libcxx to current version.
Missing string.h functionality.
Handle negative zero values correctly.

This handles the situation when they're part of a global variable
whether it just be a float/double or embedded within a struct.

Fixes #1898.
Add strtod(), wcstod(), wcstol() and friends.

This implementation of strtod() replaces the old as it implements
support for parsing hex constants which is needed by various tests.
Add gamma functions.
Make lgamma and friends work, add test.

We can't use weak aliases on variables in emscripten, so get rid of __signgam
and just use signgam.
Another test for negative zero and hex floats.
Add lots of math functions.
Move scalbn to libc to fix broken functionality. Disable test on x86.
Bump version.
Merge pull request #2004 from waywardmonkeys/updates

Updates