Core/Misc: Avoid Helgrind reporting libstdc++ false positive race conditions

cmake/showoptions.cmake

@@ -93,5 +93,13 @@ if ( NOJEM )
   message(" *** DO NOT DISABLE IT UNLESS YOU KNOW WHAT YOU'RE DOING!")
 endif()
 
+if ( HELGRIND )
+  message("")
+  message(" *** HELGRIND - WARNING!")
+  message(" *** Please specify the valgrind include directory in VALGRIND_INCLUDE_DIR option if you get build errors")
+  message(" *** Please note that this is for DEBUGGING WITH HELGRIND only!")
+  add_definitions(-DHELGRIND)
+endif()
+
 message("")