libs/libs.mk: Rework target headers.chk dependencies

There is no need to call the "headers.chk" target when it isn't
wanted, so it never need to be .PHONY.

Also, there is no more reason to separate the prerequisites from the
recipe.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

tools/libs/libs.mk

@@ -55,22 +55,20 @@ $(PKG_CONFIG_LOCAL): PKG_CONFIG_INCDIR = $(XEN_INCLUDE)
 $(PKG_CONFIG_LOCAL): PKG_CONFIG_LIBDIR = $(CURDIR)
 
 .PHONY: all
-all: headers.chk $(TARGETS) $(PKG_CONFIG_LOCAL) libxen$(LIBNAME).map $(LIBHEADERS)
+all: $(TARGETS) $(PKG_CONFIG_LOCAL) libxen$(LIBNAME).map $(LIBHEADERS)
 
 ifneq ($(NO_HEADERS_CHK),y)
-headers.chk:
+all: headers.chk
+
+headers.chk: $(LIBHEADERS) $(AUTOINCS)
 	for i in $(filter %.h,$^); do \
 	    $(CC) -x c -ansi -Wall -Werror $(CFLAGS_xeninclude) \
 	          -S -o /dev/null $$i || exit 1; \
 	    echo $$i; \
 	done >$@.new
 	mv $@.new $@
-else
-.PHONY: headers.chk
 endif
 
-headers.chk: $(LIBHEADERS) $(AUTOINCS)
-
 headers.lst: FORCE
 	@{ set -e; $(foreach h,$(LIBHEADERS),echo $(h);) } > $@.tmp
 	@$(call move-if-changed,$@.tmp,$@)