Makefile: reorder a few phony and variable declarations

Makefile

@@ -54,6 +54,7 @@ include stdlib/StdlibModules
 
 CAMLC=$(CAMLRUN) boot/ocamlc -g -nostdlib -I boot -use-prims byterun/primitives
 CAMLOPT=$(CAMLRUN) ./ocamlopt -g -nostdlib -I stdlib -I otherlibs/dynlink
+ARCHES=amd64 i386 arm arm64 power sparc s390x
 INCLUDES=-I utils -I parsing -I typing -I bytecomp -I middle_end \
         -I middle_end/base_types -I asmcomp -I driver -I toplevel
 
@@ -1137,11 +1138,10 @@ partialclean::
 
 beforedepend:: $(ARCH_SPECIFIC)
 
-.PHONY: check_arch check_all_arches
-
 # This rule provides a quick way to check that machine-dependent
 # files compiles fine for a foreign architecture (passed as ARCH=xxx).
 
+.PHONY: check_arch
 check_arch:
 	@echo "========= CHECKING asmcomp/$(ARCH) =============="
 	@rm -f $(ARCH_SPECIFIC) asmcomp/emit.ml asmcomp/*.cm*
@@ -1149,8 +1149,7 @@ check_arch:
 	            >/dev/null
 	@rm -f $(ARCH_SPECIFIC) asmcomp/emit.ml asmcomp/*.cm*
 
-ARCHES=amd64 i386 arm arm64 power sparc s390x
-
+.PHONY: check_all_arches
 check_all_arches:
 	@STATUS=0; \
 	 for i in $(ARCHES); do \