Update to new Rack SDK. Update to more robust isl resource for building toolchains.

Makefile

@@ -16,7 +16,7 @@ export JOBS :=
 export JOBS_CT_NG :=
 endif
 
-RACK_SDK_VERSION := 2.git.219bbaf1
+RACK_SDK_VERSION := 2.git.588342d7
 
 all: toolchain-all
 
@@ -40,7 +40,7 @@ toolchain-lin: $(toolchain-lin)
 $(toolchain-lin): $(crosstool-ng)
 	# HACK until crosstool-ng has fixed its mirror for isl library
 	-mkdir /home/build/src
-	cd /home/build/src && wget ftp.halifax.rwth-aachen.de/gentoo/distfiles/isl-0.24.tar.xz
+	cd /home/build/src && wget http://deb.debian.org/debian/pool/main/i/isl/isl_0.24.orig.tar.xz && mv isl_0.24.orig.tar.xz isl-0.24.tar.xz
 	ct-ng x86_64-ubuntu16.04-linux-gnu
 	CT_PREFIX="$(LOCAL_DIR)" ct-ng build$(JOBS_CT_NG)
 	rm -rf .build .config build.log
@@ -55,7 +55,7 @@ toolchain-win: $(toolchain-win)
 $(toolchain-win): $(crosstool-ng)
 	# HACK until crosstool-ng has fixed its mirror for isl library
 	-mkdir /home/build/src
-	cd /home/build/src && wget ftp.halifax.rwth-aachen.de/gentoo/distfiles/isl-0.24.tar.xz
+	cd /home/build/src && wget http://deb.debian.org/debian/pool/main/i/isl/isl_0.24.orig.tar.xz && mv isl_0.24.orig.tar.xz isl-0.24.tar.xz
 	ct-ng x86_64-w64-mingw32
 	CT_PREFIX="$(LOCAL_DIR)" ct-ng build$(JOBS_CT_NG)
 	rm -rf .build .config build.log /home/build/src