Previously WireCmd.h/cpp that is used in wire_autogen wasn't included in
the sources, causing a link error on some platforms.
With WireCmd.* moved in the EXTRA_SOURCES, the nxt_wire target didn't
contain any non-header file and caused a link error on OSX. Fix it by
properly splitting the declaration and implementation of
TerribleCommandBuffer in a .h and .cpp file.
For shared library to work on Windows to work, we need to add
declspec(export) and declspec(import) annotations to the symbols to
export. This fixes the problem by making all libraries static on
Windows, but we'll need to revisit and do proper symbol exports.
Corentin Wallez