meson: enable -Wzero-length-bounds

This will warn if fake flexible arrays are re-introduced. I'm not using
-Werror=… because we may still get warnings when compiling against old kernel
headers. We can crank this up to error later.

meson.build

@@ -389,6 +389,7 @@ possible_common_cc_flags = [
         '-Wsuggest-attribute=noreturn',
         '-Wunused-function',
         '-Wwrite-strings',
+        '-Wzero-length-bounds',
 
         # negative arguments are correctly detected starting with meson 0.46.
         '-Wno-error=#warnings',  # clang