message: Allow setting tinyxml2 source directory
  * Allow setting tinyxml2 source directory
  This CL adds a build flag to allow the tinyxml2 source directory to
  exist outside the Vulkan-HPP source tree.
  * Add quotes around path
diff: @@ -52,12 +52,16 @@ set(SOURCES
  VulkanHppGenerator.cpp
  )
  +if (NOT DEFINED VULKAN_HPP_TINYXML2_SRC_DIR)
  + set(VULKAN_HPP_TINYXML2_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/tinyxml2")
  +endif()
  +
  set(TINYXML2_SOURCES
  - tinyxml2/tinyxml2.cpp
  + ${VULKAN_HPP_TINYXML2_SRC_DIR}/tinyxml2.cpp
  )
  set(TINYXML2_HEADERS
  - tinyxml2/tinyxml2.h
  + ${VULKAN_HPP_TINYXML2_SRC_DIR}/tinyxml2.h
  )
  source_group(headers FILES ${HEADERS})
  @@ -75,7 +79,7 @@ add_executable(VulkanHppGenerator
  set_property(TARGET VulkanHppGenerator PROPERTY CXX_STANDARD 11)
  -target_include_directories(VulkanHppGenerator PRIVATE "${CMAKE_SOURCE_DIR}/tinyxml2")
  +target_include_directories(VulkanHppGenerator PRIVATE ${VULKAN_HPP_TINYXML2_SRC_DIR})
  option (SAMPLES_BUILD OFF)
  if (SAMPLES_BUILD)
  