Build: Fix gcc pch builds

dep/boost/CMakeLists.txt

@@ -38,6 +38,11 @@ if(WIN32)
   set(Boost_USE_STATIC_RUNTIME     OFF)
 endif()
 
+if (CMAKE_VERSION VERSION_LESS "3.16.0")
+  # boost's own cmake file adds extra compile definitions that cotire fails to pick up
+  set(Boost_NO_BOOST_CMAKE ON)
+endif()
+
 include (CheckCXXSourceCompiles)
 
 check_cxx_source_compiles("