Print the "listening" message only in lldb compat mode.

This message is useless otherwise, so get rid of it.
Add build of the fault handler to CMake.
Get rid of constexpr.

This is not supported by MSVC pre-2014.
Correct the definition of a macro

The macro was not in use previously.  A missing closing parenthesis results in
the file being unusable.
Consolidate architecture definition

Create a new definition for the architecture.  This allows us to use the same
definition irrespective of the compiler used.  MSVC defines _M_* macros, whilst
gcc and clang define __*__ macros.  Adjust the codebase to use the new ARCH_*
macros defined in Base.h.
Use __FUNCTION__ instead of __func__.

This is supported by more compilers.
Create a DS2_UNREACHABLE macro

__builtin_trap is not always available.  The particular use of it was indented
to indicate that the code path is not reachable.  Create a DS2_UNREACHABLE macro
to aid in marking the location as such across various compilers.