Fixed BUILD scripts for gcc 6.x

Added also -DTRASH_FREE_MEMORY to valgrind builds

BUILD/SETUP.sh

@@ -141,7 +141,7 @@ elif [ "x$warning_mode" = "xmaintainer" ]; then
   debug_extra_cflags="-g3"
 else
 # Both C and C++ warnings
-  warnings="-Wall -Wextra -Wunused -Wwrite-strings -Wno-uninitialized -Wno-strict-aliasing -Wimplicit-fallthrough=2"
+  warnings="-Wall -Wextra -Wunused -Wwrite-strings -Wno-uninitialized -Wno-strict-aliasing"
 
 # For more warnings, uncomment the following line
 # warnings="$warnings -Wshadow"
@@ -160,7 +160,10 @@ fi
 # Override -DFORCE_INIT_OF_VARS from debug_cflags. It enables the macro
 # UNINIT_VAR(), which is only useful for silencing spurious warnings
 # of static analysis tools. We want UNINIT_VAR() to be a no-op in Valgrind.
-valgrind_flags="-DHAVE_valgrind -USAFEMALLOC"
+# TRASH_FREE_MEMORY is enabled so that we can find wrong memory accesses
+# even when running a test without valgrind
+#
+valgrind_flags="-DHAVE_valgrind -USAFEMALLOC -DTRASH_FREE_MEMORY"
 valgrind_flags="$valgrind_flags -UFORCE_INIT_OF_VARS -Wno-uninitialized"
 valgrind_flags="$valgrind_flags -DMYSQL_SERVER_SUFFIX=-valgrind-max"
 valgrind_configs="--with-valgrind"
@@ -252,6 +255,11 @@ if test `$CC -v 2>&1 | tail -1 | sed 's/ .*$//'` = 'gcc' ; then
   then
     debug_cflags="$debug_cflags -DFORCE_INIT_OF_VARS -Wuninitialized"
   fi
+  if (test '(' "$GCCV1" -gt '6' ')')
+  then
+    c_warnings="$c_warnings -Wimplicit-fallthrough=2"
+    cxx_warnings="$cxx_warnings -Wimplicit-fallthrough=2"
+  fi
 fi