Enable implicit locking for RBT operations

There are a lot of possible memory overruns reported by helgrind
coming from rbt_* operations without this flag.

Author: evgenyz

CMakeLists.txt

@@ -535,7 +535,7 @@ if (MSVC)
 endif()
 
 if (${CMAKE_C_COMPILER_ID} STREQUAL "GNU" OR ${CMAKE_C_COMPILER_ID} STREQUAL "Clang")
-	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -pipe -W -Wall -Wnonnull -Wshadow -Wformat -Wundef -Wno-unused-parameter -Wmissing-prototypes -Wno-unknown-pragmas -Wno-int-conversion -Werror=implicit-function-declaration -D_GNU_SOURCE -std=c99")
+	set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -pipe -W -Wall -Wnonnull -Wshadow -Wformat -Wundef -Wno-unused-parameter -Wmissing-prototypes -Wno-unknown-pragmas -Wno-int-conversion -Werror=implicit-function-declaration -D_GNU_SOURCE -DRBT_IMPLICIT_LOCKING=1 -std=c99")
 	add_link_options(-Wl,-z,now)
 endif()
 if(${CMAKE_SYSTEM_NAME} STREQUAL "FreeBSD")