MDEV-36542: apply clang -Werror=uninitialized to catch dubious initializations

clang has rather correct error detection in its
implementation of the -Werror=uninitialized* set of C/CXX flags.

Use them by default.

Author: grooverdan

cmake/maintainer.cmake

@@ -68,6 +68,14 @@ IF(CMAKE_C_COMPILER_ID STREQUAL "GNU" AND CMAKE_C_COMPILER_VERSION VERSION_LESS
   SET(MY_ERROR_FLAGS ${MY_ERROR_FLAGS} -Wno-error=non-virtual-dtor) # gcc bug 7302
 ENDIF()
 
+FOREACH(LANG C CXX)
+  IF(CMAKE_${LANG}_COMPILER_ID MATCHES "Clang")
+    MY_CHECK_AND_SET_COMPILER_FLAG(-Werror=uninitialized-explicit-init)
+    MY_CHECK_AND_SET_COMPILER_FLAG(-Werror=uninitialized-const-reference)
+    SET(CMAKE_${LANG}_FLAGS "${CMAKE_${LANG}_FLAGS} -Werror=uninitialized")
+  ENDIF()
+ENDFOREACH()
+
 IF(MYSQL_MAINTAINER_MODE MATCHES "OFF|WARN")
   RETURN()
 ELSEIF(MYSQL_MAINTAINER_MODE MATCHES "AUTO")