convert Windows paths in include directories to CMake paths

CMake/cotire.cmake

@@ -626,6 +626,25 @@ function (cotire_get_target_include_directories _config _language _target _inclu
 	if (CMAKE_${_language}_IMPLICIT_INCLUDE_DIRECTORIES)
 		list (REMOVE_ITEM _includeDirs ${CMAKE_${_language}_IMPLICIT_INCLUDE_DIRECTORIES})
 	endif()
+	if (WIN32)
+		# convert Windows paths in include directories to CMake paths
+		if (_includeDirs)
+			set (_paths "")
+			foreach (_dir ${_includeDirs})
+				file (TO_CMAKE_PATH "${_dir}" _path)
+				list (APPEND _paths "${_path}")
+			endforeach()
+			set (_includeDirs ${_paths})
+		endif()
+		if (_systemIncludeDirs)
+			set (_paths "")
+			foreach (_dir ${_systemIncludeDirs})
+				file (TO_CMAKE_PATH "${_dir}" _path)
+				list (APPEND _paths "${_path}")
+			endforeach()
+			set (_systemIncludeDirs ${_paths})
+		endif()
+	endif()
 	if (COTIRE_DEBUG AND _includeDirs)
 		message (STATUS "Target ${_target} include dirs: ${_includeDirs}")
 	endif()