CLN/BUILD: Fix clang warnings on build
Here's the [output](https://gist.github.com/TomAugspurger/7232405) from the current master. I could try to clean some of the warnings up someday _if there's any interest_; a decent excuse to look through the source code.

A lot of the warnings look similar:
- deprecated numpy API
- warning: static variable 'PyArray_API' is used in an inline function with external linkage [-Wstatic-in-inline]
- warning: comparison of constant -1 with expression of type 'PANDAS_DATETIMEUNIT' is always true
- warning: format specifies type 'long' but the argument has type 'long long' [-Wformat]
- various unused functions

What do things look like with gcc (and whatever windows uses)?
