Bug#35311140 Build failure with Homebrew rapidjson installed & symlinked

On MacOS, If Homebrew rapidjson is installed, then build fails. Note that
even -DWITH_RAPIDJSON=bundled does not help, and the only workaround is brew
unlink rapidjson.

This is a regression from
    Bug#35006191 Convert rapidjson to a cmake interface library
which removed the global
    INCLUDE_DIRECTORIES(BEFORE SYSTEM ${RAPIDJSON_INCLUDE_DIR})

It turns out we need this on MacOS to avoid accidental #include of
rapidjson headers from Homebrew rather than the bundled code in
extra/rapidjson.

Backported to 8.0
(cherry picked from commit ac364d25c0fdd10eaaecc5bb935e85c592879f7e)
Change-Id: Id737953d05ea77f35de656067f594b47a7c7ba51

Author: Tor Didriksen

cmake/rapidjson.cmake

@@ -86,6 +86,10 @@ MACRO (MYSQL_CHECK_RAPIDJSON)
 
   IF (WITH_RAPIDJSON STREQUAL "bundled")
     SET(RAPIDJSON_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/extra/rapidjson/include)
+    # We must include this first, in case we use other Homebrew libraries.
+    IF(APPLE)
+      INCLUDE_DIRECTORIES(BEFORE SYSTEM ${RAPIDJSON_INCLUDE_DIR})
+    ENDIF()
   ELSEIF(WITH_RAPIDJSON STREQUAL "system")
     FIND_SYSTEM_RAPIDJSON()
     IF (NOT SYSTEM_RAPIDJSON_FOUND)