Racket actually has been ported to all the architectures, just without JIT.

FUTURES actually seems to require JIT (errors with JIT-related object files
when compiling on aarch64), so move FUTURES to the amd64/i386 only section.

aarch64 also required a define.  Submitted upstream:

  https://github.com/racket/racket/pull/2187

While here, clarify the status on powerpc64 (tested by linimon).

PR:		230019
Submitted by:	greg at unrelenting dot technology
Approved by:	portmgr (tier-2 blanket)

lang/racket/Makefile

@@ -22,13 +22,11 @@ LIB_DEPENDS=	libffi.so:devel/libffi		\
 		libcairo.so:graphics/cairo	\
 		libpng.so:graphics/png
 
-BROKEN_powerpc64=	fails to build: jit.c: 'JIT_LOCAL4' undeclared (first use in this function)
+IGNORE_powerpc64=	./lightning/lightning.h:81:2: GNU lightning does not support the current target
 BROKEN_FreeBSD_10_i386=	segfaults during build
 BROKEN_FreeBSD_11_i386=	segfaults during build
 BROKEN_FreeBSD_12_i386=	segfaults during build
 BROKEN_FreeBSD_13_i386=	segfaults during build
-NOT_FOR_ARCHS=		aarch64 armv6 armv7 sparc64
-NOT_FOR_ARCHS_REASON=	not yet ported to this arch
 
 MAKE_JOBS_UNSAFE=yes
 
@@ -48,10 +46,10 @@ USE_GNOME=	cairo pango
 OPTIONS_DEFINE=	DOCS FUTURES
 OPTIONS_DEFAULT=FUTURES
 
-OPTIONS_DEFINE_amd64=	JIT
-OPTIONS_DEFINE_i386=	JIT
-OPTIONS_DEFAULT_amd64=	JIT
-OPTIONS_DEFAULT_i386=	JIT
+OPTIONS_DEFINE_amd64=	JIT FUTURES
+OPTIONS_DEFINE_i386=	JIT FUTURES
+OPTIONS_DEFAULT_amd64=	JIT FUTURES
+OPTIONS_DEFAULT_i386=	JIT FUTURES
 
 FUTURES_DESC=	Enable futures
 JIT_DESC=	Enable JIT compiler

lang/racket/files/patch-src_racket_sconfig.h

@@ -0,0 +1,10 @@
+--- src/racket/sconfig.h.orig	2018-10-30 18:06:25 UTC
++++ src/racket/sconfig.h
+@@ -350,7 +350,6 @@
+ #  define SCHEME_PLATFORM_LIBRARY_SUBPATH "aarch64-freebsd"
+ # elif defined(__powerpc__)
+ #  define SCHEME_PLATFORM_LIBRARY_SUBPATH "ppc-freebsd"
+-#  define MZ_USE_JIT_PPC
+ # else
+ #  error Unported platform.
+ # endif