cflags: add -Wdeclaration-after-statement

This allows people working on the code to spot the
most common error that breaks the MSVC build

Signed-off-by: Steve Markgraf <steve@steve-m.de>

CMakeLists.txt

@@ -52,6 +52,7 @@ if(CMAKE_COMPILER_IS_GNUCC AND NOT WIN32)
     ADD_DEFINITIONS(-Wno-unused-parameter)
     ADD_DEFINITIONS(-Wno-unused)
     ADD_DEFINITIONS(-Wsign-compare)
+    ADD_DEFINITIONS(-Wdeclaration-after-statement)
     #http://gcc.gnu.org/wiki/Visibility
     add_definitions(-fvisibility=hidden)
 endif()

configure.ac

@@ -62,7 +62,7 @@ AC_SUBST(SYMBOL_VISIBILITY)
 
 AC_MSG_CHECKING(whether compiler understands -Wall)
 old_CFLAGS="$CFLAGS"
-CFLAGS="$CFLAGS -Wall -Wextra -Wno-unused-parameter -Wno-unused -Wsign-compare"
+CFLAGS="$CFLAGS -Wall -Wextra -Wno-unused-parameter -Wno-unused -Wsign-compare -Wdeclaration-after-statement"
 AC_TRY_COMPILE([],[],
   AC_MSG_RESULT(yes),
   AC_MSG_RESULT(no)