just in case old linux is used, add _GNU_SOURCE preprocessor constant to be...

just in case old linux is used, add _GNU_SOURCE preprocessor constant to be able to see pthread_rwlock_t

storage/innobase/CMakeLists.txt

@@ -22,7 +22,7 @@ INCLUDE(CheckCSourceRuns)
 # OS tests
 IF(UNIX)
   IF(CMAKE_SYSTEM_NAME STREQUAL "Linux")
-    ADD_DEFINITIONS("-DUNIV_LINUX")
+    ADD_DEFINITIONS("-DUNIV_LINUX -D_GNU_SOURCE=1")
   ELSEIF(CMAKE_SYSTEM_NAME MATCHES "HP*")
     ADD_DEFINITIONS("-DUNIV_HPUX -DUNIV_MUST_NOT_INLINE")
   ELSEIF(CMAKE_SYSTEM_NAME STREQUAL "AIX")