MDEV-6305 - UNINIT_VAR emits code in non-debug builds

Reverted workaround for gcc bug, which was fixed 3 years ago:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

configure.cmake

@@ -55,7 +55,7 @@ ENDIF()
 
 # Always enable -Wall for gnu C/C++
 IF(CMAKE_COMPILER_IS_GNUCXX AND NOT CMAKE_CXX_FLAGS MATCHES ".*-Wall.*")
-  SET(CMAKE_CXX_FLAGS "-Wall ${CMAKE_CXX_FLAGS} -Wall -Wno-unused-parameter")
+  SET(CMAKE_CXX_FLAGS "-Wall ${CMAKE_CXX_FLAGS} -Wall -Wno-unused-parameter -Wno-init-self")
 ENDIF()
 IF(CMAKE_COMPILER_IS_GNUCC AND NOT CMAKE_C_FLAGS MATCHES ".*-Wall.*")
   SET(CMAKE_C_FLAGS "-Wall ${CMAKE_C_FLAGS} -Wall")

include/my_global.h

@@ -480,16 +480,14 @@ extern "C" int madvise(void *addr, size_t len, int behav);
 
 /*
    Suppress uninitialized variable warning without generating code.
-
-   The _cplusplus is a temporary workaround for C++ code pending a fix
-   for a g++ bug (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772).
 */
-#if defined(_lint) || defined(FORCE_INIT_OF_VARS) || \
-    defined(__cplusplus) || !defined(__GNUC__)
-#define UNINIT_VAR(x) x= 0
-#else
+#if defined(__GNUC__)
 /* GCC specific self-initialization which inhibits the warning. */
 #define UNINIT_VAR(x) x= x
+#elif defined(_lint) || defined(FORCE_INIT_OF_VARS)
+#define UNINIT_VAR(x) x= 0
+#else
+#define UNINIT_VAR(x) x
 #endif
 
 #if !defined(HAVE_UINT)