gnu: http-parser: Fix build on i686-linux.

Fixes a regression introduced in
c11fcc6aa2, whereby 'http-parser' would
fail to build on i686.

* gnu/packages/web.scm (http-parser)[source](modules, snippet): New
fields.

gnu/packages/web.scm

@@ -5163,7 +5163,16 @@ into your tests.  It automatically starts up a HTTP server in a separate thread
               (file-name (git-file-name name version))
               (sha256
                (base32
-                "12ilmjma6vmlm2kl23fx5pbi226x098gljgxpx3h2kmq8pg2lm28"))))
+                "12ilmjma6vmlm2kl23fx5pbi226x098gljgxpx3h2kmq8pg2lm28"))
+              (modules '((guix build utils)))
+              (snippet
+               '(begin
+                  ;; There are signedness errors that trigger on 32-bit
+                  ;; platforms that trigger, and '-Werror' leads to build
+                  ;; failures.
+                  (substitute* "Makefile"
+                    (("-Werror") ""))
+                  #t))))
     (build-system gnu-build-system)
     (arguments
      `(#:test-target "test"