Add 'download-checkra1n' target

Makefile

@@ -23,7 +23,7 @@ export SRC DEP CC CFLAGS LDFLAGS LIBS
 
 all: palera1n
 
-palera1n:
+palera1n: download-checkra1n
 	$(MAKE) -C src
 
 clean:
@@ -48,7 +48,10 @@ macos-dist:
 	$(STRIP) palera1n-macos
 	codesign -s - --force palera1n-macos
 
+download-checkra1n:
+	$(MAKE) -C src checkra1n-macos checkra1n-linux-arm64 checkra1n-linux-armel checkra1n-linux-x86 checkra1n-linux-x86_64
+
 distclean: clean
-	rm -rf palera1n-* palera1n*.dSYM
+	rm -rf palera1n-* palera1n*.dSYM src/checkra1n-*
 
 .PHONY: all palera1n clean

src/Makefile

@@ -3,6 +3,10 @@ all: palera1n
 OBJECTS = main.o dfuhelper.o lockdown_helper.o devhelper.o exec_checkra1n.o pongo_usb.o checkra1n.o
 LIPO = lipo
 
+checkra1n-%:
+	curl -LO https://assets.checkra.in/downloads/preview/0.1337.1/$@
+	chmod 755 $@
+
 checkra1n: checkra1n-macos
 ifneq (,$(findstring arm64, $(CFLAGS)))
 	$(LIPO) -thin arm64 -output checkra1n checkra1n-macos