Port DXC to Linux [umbrella issue]

[ehsannas]

This is an umbrella issue to track all the work that's needed to be done related to porting DXC to Linux.

• Make all necessary CMake changes in order to compile the project on Linux.
• Disable all the SAL Annotations used throughout the code
  • Usages such as: _In_, _Out_, _Field_size_(...), etc.
  • Full list at WinSAL.h
• Define Windows-specific macros that are used throughout the code
  • Examples: ATLASSERT, STDAPI, UNREFERENCED_PARAMETER, etc.
  • Full list at WinMacros.h
• Define the Windows-specific types
  • Simple cases such as: BOOLEAN, WORD, BYTE, LPSTR, PCWSTR, HMODULE, HINSTANCE, etc.
  • More complicated cases: LARGE_INTEGER, STATSTG, etc.
  • Defined in WinTypes.h
• Implement "adapter" classes to fill the void of unknown classes on Linux.
  • CAllocator. Provides Allocate, Free, and Reallocate interfaces using malloc, free, and realloc.
  • Converters for strings (CW2A, CW2AEX, CA2W, CA2WEX) ([linux-port] CA2W and CA2WEX #172)
  • Smart pointer for heap memory (CHeapPtr with methods such as Allocate, Attach, Detach, Free, etc.)
  • CSimpleArray. Provides functionalities similar to std::vector
  • COM related: IUnknown, CComPtrBase, CComPtr, IMalloc
  • Stream related: IStream, ISequentialStream
• Implement a method to provide QueryInterface and __uuidof(...) functionality.
• Provide an MSFileSystem impl for Unix.
• Replace hardcoded usages of DLL filenames (e.g. dxcompiler.dll) with .so equivalents (e.g. libdxcompiler.so)
• Implement some Windows-specific functions:
  • MultiByteToWideChar
  • WideCharToMultiByte
  • Replace LoadLibrary, FreeLibrary, GetProcAddress (using dlopen, dlclose, dlsym)
  • Replace CheckThreadId with sys::SmartScopedReader in PassRegistry.
• File I/O and Console I/O -> Must revisit.
• Fix general compilation issues
  • Fix linking issues related to usages of extern
  • Avoid using global static variables in header files ([linux-port] Fix a handful of warnings in headers #192)
  • ULL to UI64
  • Make std::hex work with DiagnosticPrinter ([linux-port] Fix DiagnosticPrinter use of std::hex #179)
  • Use llvm::make_unique rather than std::make_unique
  • Use standard c++ override rather than _override
• Implement thread-local storage (instead of TlsAlloc, TlsFree,TlsGetValue, TlsSetValue) ([linux-port] Thread-local storage #173)
• Launch Appveyor and Travis buildbots. Appveyor to provide Windows builds and Travis to provide clang and gcc builds on Linux. ([linux-port] Fix Appveyor and Travis for the Linux branch #177)
• Minimal supported GCC/Clang version ([linux] Minimum supported GCC/Clang version #196)
  • GCC 5 support ([linux-port] Allow GCC5 compiling #197)
• Resolve platform-specific issues in dxc.cpp in order to get the DXC executable working on Linux.
• Get SPIR-V CodeGen test working on Linux ([linux-port] Get SPIRV CodeGen tests running. #193)
• Use alternate thread-safe mechanisms (Thread-safe mechanisms not fully implemented on non-Win32 #198)
  • Use llvm::sys::Atomic* instead of InterlockedIncrement, InterlockedDecrement
  • Find an alternative for CriticalSection
• Address compiler warnings (Reduce or eliminate warnings on GCC and Clang #206)
• To be continued.