Compilation with warnings-as-errors should be optional

[ekilmer]

Compiling with warnings-as-errors is fine if your compiler doesn't change, but as new compilers are released, new warnings might pop up and fail a compilation for an end-user.

The user should be able to turn on warnings-as-errors through a CMake option, and this option should be disabled by default in the CMakeLists.txt file but enabled for all CI runs.

The associated compiler flags are -Werror for gcc and clang, and /WX for MSVC compilers. These are located in https://github.com/trailofbits/pe-parse/blob/master/cmake/compilation_flags.cmake