Mat 468: patch up sources following build system upgrade

This minor patch set is the result of weeks of work upgrading the entire build system.
We now have dedicated machines for building the 64 and 32 bit windows variants.
GCC is globally upgraded to version 4.9.1.
CMake is globally upgraded to 3.0+.

The native library loader and assembler system is patched with regards to the new GCC. Whilst doing this I unified the OS labelling scheme across all sources as:
```
"w64" = 64bit Windows
"w32" = 32bit Windows
"lnx" = Linux
"osx" = OSX
```
It also transpired in the upgrade of GCC that there were a few instances of signed/unsigned int comparison, I have duly patched them. It also appears the Google's gtest code does not compile with `-Wsign-compare` which is applied via `-Wall`. I tried upgrading gtest to version 1.7, the same issue is present. I've therefore added in an override to `-Wall` of `-Wno-sign-compare` and noted it as something we need to look at [MAT-469](https://opengamma.atlassian.net/browse/MAT-469).

Code coverage:
No material change. The minor edits are all in system level places.

Given that this is to get gtest to compile, can it be pushed into the gtest CMake stuff so it doesn't get applied to the rest of our codebase? I think a suitable place would probably be in its `config_compiler_and_linker` macro in `cmake\internal_utils.cmake`.