Refactor common Reactor implementations

Some functions in LLVMReactor.cpp and SubzeroReactor.cpp were identical
and have been moved into a common Reactor.cpp.

Bug swiftshader:21

Change-Id: Ib079757f9e35f83b1103e2791227f02775e034d3
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/27068
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>

src/Reactor/Reactor.vcxproj

diff --git a/src/Reactor/Reactor.vcxproj b/src/Reactor/Reactor.vcxproj
index b26b32f..60c15c5 100644
--- a/src/Reactor/Reactor.vcxproj
+++ b/src/Reactor/Reactor.vcxproj
@@ -289,6 +289,7 @@
     <ClCompile Include="LLVMRoutineManager.cpp" />

     <ClCompile Include="LLVMReactor.cpp" />

     <ClCompile Include="ExecutableMemory.cpp" />

+    <ClCompile Include="Reactor.cpp" />

     <ClCompile Include="Routine.cpp" />

     <ClCompile Include="Thread.cpp" />

   </ItemGroup>