contrib: gmp: Patch away the ansi2knr mentionings

The latest automake versions (as built by extras/tools) have
removed support for ansi2knr altogether, so this is required for
reconfiguration to work. We still need to do the reconf since the
host system ANSI check in the tarball is broken.

Signed-off-by: Martin Storsjö <martin@martin.st>