message: Re-introduced the custom build defines
  The ability to use custom build defines were removed in commit:
  This commit will reintroduce this feature, but using a prefixed variable
  name.
diff: @@ -23,6 +23,9 @@ cmake_dependent_option(PUGIXML_BUILD_TESTS
  "Build pugixml tests" OFF
  "BUILD_TESTING;CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR" OFF)
  +# Custom build defines
  +set(PUGIXML_BUILD_DEFINES CACHE STRING "Build defines")
  +
  option(PUGIXML_BUILD_SHARED_AND_STATIC_LIBS "Build both shared and static libraries" OFF)
  # Expose option to build PUGIXML as static even when the global BUILD_SHARED_LIBS variable is set
  @@ -44,6 +47,12 @@ if (NOT DEFINED CMAKE_CXX_STANDARD)
  set(CMAKE_CXX_STANDARD 11)
  endif()
  +if (DEFINED PUGIXML_BUILD_DEFINES)
  + foreach(DEFINE ${PUGIXML_BUILD_DEFINES})
  + add_definitions("-D" ${DEFINE})
  + endforeach()
  +endif()
  +
  if (PUGIXML_USE_POSTFIX)
  set(CMAKE_RELWITHDEBINFO_POSTFIX _r)
  set(CMAKE_MINSIZEREL_POSTFIX _m)
  