Use "command -v" instead of "which"

The "which" command has been deprecated in debianutils, and while other
distributions still ship it, "command -v" is in POSIX and implemented
without external packages.

Author: mid-kid

Makefile

@@ -35,7 +35,7 @@ pokecrystal11_vc_obj    := $(rom_obj:.o=11_vc.o)
 
 ### Build tools
 
-ifeq (,$(shell which sha1sum))
+ifeq (,$(shell command -v sha1sum 2>/dev/null))
 SHA1 := shasum
 else
 SHA1 := sha1sum