Fix the fix.

OBS-URL: https://build.opensuse.org/package/show/devel:gcc/gdb?expand=0&rev=179

gdb.spec

@@ -590,7 +590,7 @@ export CFLAGS="$RPM_OPT_FLAGS"
 # warn about unknown -Wno- flags, _except_ if there are other
 # diagnostics as well, so let's force an uninitialized use warning
 # and grep for the diagnostic about the -Wno flag:
-if echo "int foo(void) { int a; return a;} " | \
+if ! echo "int foo(void) { int a; return a;} " | \
    $CC  -x c -c - -o /dev/null -W -Wno-implicit-fallthrough 2>&1 | \
    grep Wno-implici >/dev/null; then
   CFLAGS="$CFLAGS -Wno-implicit-fallthrough"