Merge of the fix for BUG#57933 "add -Wdeclaration-after-statement to gcc builds"

from 5.1; extended here to Cmake builds.

CMakeLists.txt

@@ -115,18 +115,27 @@ ENDIF()
 # Control aspects of the development environment which are
 # specific to MySQL maintainers and developers.
 #
+INCLUDE (CheckCCompilerFlag)
 OPTION(MYSQL_MAINTAINER_MODE "MySQL maintainer-specific development environment" OFF)
 # Whether the maintainer mode should be enabled.
 IF(MYSQL_MAINTAINER_MODE)
   IF(CMAKE_COMPILER_IS_GNUCC)
+    CHECK_C_COMPILER_FLAG("-Wdeclaration-after-statement" HAVE_DECLARATION_AFTER_STATEMENT)
+    IF(HAVE_DECLARATION_AFTER_STATEMENT)
+      SET(MY_MAINTAINER_DECLARATION_AFTER_STATEMENT "-Wdeclaration-after-statement")
+    ENDIF()
     SET(MY_MAINTAINER_C_WARNINGS
-        "-Wall -Wextra -Wunused -Wwrite-strings -Wno-strict-aliasing -Werror"
-        CACHE STRING "C warning options used in maintainer builds.")
+        "-Wall -Wextra -Wunused -Wwrite-strings -Wno-strict-aliasing -Werror")
   ENDIF()
   IF(CMAKE_COMPILER_IS_GNUCXX)
     SET(MY_MAINTAINER_CXX_WARNINGS "${MY_MAINTAINER_C_WARNINGS} -Wno-unused-parameter"
         CACHE STRING "C++ warning options used in maintainer builds.")
   ENDIF()
+  IF(CMAKE_COMPILER_IS_GNUCC)
+    SET(MY_MAINTAINER_C_WARNINGS
+        "${MY_MAINTAINER_C_WARNINGS} ${MY_MAINTAINER_DECLARATION_AFTER_STATEMENT}"
+        CACHE STRING "C warning options used in maintainer builds.")
+  ENDIF()
   # Do not make warnings in checks into errors.
   IF(CMAKE_COMPILER_IS_GNUCC AND CMAKE_COMPILER_IS_GNUCXX)
     SET(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -Wno-error")

config/ac-macros/maintainer.m4

@@ -19,6 +19,7 @@ AC_DEFUN([MY_MAINTAINER_MODE_WARNINGS], [
   AS_IF([test "$GCC" = "yes"], [
     C_WARNINGS="-Wall -Wextra -Wunused -Wwrite-strings -Wno-strict-aliasing -Werror"
     CXX_WARNINGS="${C_WARNINGS} -Wno-unused-parameter"
+    C_WARNINGS="${C_WARNINGS} -Wdeclaration-after-statement"
   ])
 
   # Test whether the warning options work.