Compiler support on windows

[lefticus]

This PR enables compiler support with embedded LLVM on Windows.

A squash merge might be recommended. There are many small commits as the testing was moved back and forth between Windows and Linux.

Addresses

• 48 https://github.com/lefticus/llvm-msvc

• 49

• 50

• 51

Notes

• Requires custom build of llvm for linking on MSVC (https://github.com/lefticus/llvm-msvc)
• Due to difficulty / availability of required Modelica tools, the full toolchain is not tested on Windows currently
• A new custom c standard library tool (c_bridge) is compiled and packaged with the spawn executable to avoid packaging of another C standard library, and associated licensing issues
  • c_bridge is not a standalone standard library
  • c_bridge wraps and links to the c standard library that already exists on all systems

Tested

• Simple DLL with no stdlib dependencies
• Loading of multiple DLLs at once with the same symbols
• Unloading and reloading DLLs
• Compiling multiple DLLs with the same compiler instance
• Usage of c_bridge standard library wrapper
• All provided c_bridge functions

Documentation

• CMake scripts attempts to prevent you from using the wrong version of libraries
• c_bridge.h documents the usage and design of the c_bridge library
• test_embedded_compiler.cpp tests all known features and documents some of the usage with comments and logging