auto merge of #8875 : alexcrichton/rust/fix-inner-static-library-bug, r=huonw

These commits fix bugs related to identically named statics in functions of implementations in various situations. The commit messages have most of the information about what bugs are being fixed and why.

As a bonus, while I was messing around with name mangling, I improved the backtraces we'll get in gdb by removing `__extensions__` for the trait/type being implemented and by adding the method name as well. Yay!
Remove the __log function for __log_level

Also redefine all of the standard logging macros to use more rust code instead
of custom LLVM translation code. This makes them a bit easier to understand, but
also more flexibile for future types of logging.

Additionally, this commit removes the LogType language item in preparation for
changing how logging is performed.