Some templated traits need more than just the forward declaration in order to be complied:
Reactor.hpp uses the CToReactor<> templates, and some of these specializations use the
ConstantPointer() function declared in Reactor.hpp.
Without splitting this into a declaration and implementation that sandwich Reactor.hpp,
you'll get compilation errors, so include Traits.hpp at the start of Reactor.hpp, and
Traits.inl at the end.

Bug: b/143479561
Change-Id: I15c2165325633cf01c0ae7a285d1798c128499a7
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38388Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>