Evade poratbility constraints of UPX build system

when building a tool to investigate "minimal" Mach-O executable
on Apple MacOS Big Sur using Apple M1 hardware (aarch64).
https://github.com/upx/upx/issues/567
	modified:   stub/tools/macho-snip/Makefile
	modified:   stub/tools/macho-snip/macho-snip.c
	modified:   stub/tools/macho-snip/udf.s

src/stub/tools/macho-snip/Makefile

@@ -8,13 +8,13 @@
 
 CFLAGS += -g
 
-macho-snip: macho-snip.o udf
+macho-snip: macho-snip.o
 	$(CC) $(CFLAGS) -o macho-snip macho-snip.o
 
 udf.o: udf.s
 	gcc -c $<
 
-# shortest main program;  used as an example
+# shortest main program;  used as an example for Apple Mach-O
 udf: udf.o
 	gcc --verbose -nostartfiles -o udf $<
 	codesign --remove-signature udf