llvm port does not allow REQUIRES_RTTI

The current Makefile for devel/llvm doesn't allow you to use
REQUIRES_RTTI. It's a pretty common option, and is even enabled by
default in devel/llvm-devel. I emailed the maintainer months ago and
haven't had a response or seen any changes. I've never done anything
with ports before, but my best stab at it is below.

Thanks,

-- Eric Will

--- /usr/ports/devel/llvm/Makefile      2011-04-29 11:04:29.000000000 -0400
+++ Makefile    2011-05-12 11:52:59.000000000 -0400
_at__at_ -40,6 +40,7 _at__at_
 CONFIGURE_ARGS+=       --enable-bindings=none

 OPTIONS=       ASSERTS "Enable assertions (thread unsafe)" off
+OPTIONS+=      REQUIRES_RTTI "Enable run-time type IDs (RTTI)" on

 .if defined(NOPORTDOCS)
 CONFIGURE_ARGS+=       --disable-docs
_at__at_ -70,6 +71,10 _at__at_
 .else
 CONFIGURE_ARGS+=       --disable-assertions
 .endif
+.ifdef(WITH_REQUIRES_RTTI)
+CONFIGURE_ENV+=REQUIRES_RTTI=1
+MAKE_ENV+=REQUIRES_RTTI=1
+.endif

 post-patch:
        ${REINPLACE_CMD} -e 's|\(PROJ_docsdir.*:=\).*$$|\1${DOCSDIR}|g' \