Update scripts/Makefile.fwinst to cope with older make

Also fix unwanted rebuilds of the firmware/ihex2fw tool by including
the .ihex2fw.cmd file when present.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Reported-and-tested-by: Wang Chen <wangchen@cn.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/Makefile.fwinst

@@ -28,18 +28,39 @@ endif
 installed-fw := $(addprefix $(INSTALL_FW_PATH)/,$(fw-shipped-all))
 installed-fw-dirs := $(sort $(dir $(installed-fw))) $(INSTALL_FW_PATH)/.
 
+# Workaround for make < 3.81, where .SECONDEXPANSION doesn't work.
+PHONY += $(INSTALL_FW_PATH)/$$(%) install-all-dirs
+$(INSTALL_FW_PATH)/$$(%): install-all-dirs
+	@true
+install-all-dirs: $(installed-fw-dirs)
+	@true
+
 quiet_cmd_install = INSTALL $(subst $(srctree)/,,$@)
       cmd_install = $(INSTALL) -m0644 $< $@
 
 $(installed-fw-dirs):
 	$(call cmd,mkdir)
 
-$(installed-fw): $(INSTALL_FW_PATH)/%: $(obj)/% | $(INSTALL_FW_PATH)/$$(dir %)/
+$(installed-fw): $(INSTALL_FW_PATH)/%: $(obj)/% | $(INSTALL_FW_PATH)/$$(dir %)
 	$(call cmd,install)
 
-.PHONY: __fw_install __fw_modinst FORCE
+PHONY +=  __fw_install __fw_modinst FORCE
+
+.PHONY: $(PHONY)
 
 __fw_install: $(installed-fw)
 __fw_modinst: $(mod-fw)
 
 FORCE:
+
+# Read all saved command lines and dependencies for the $(targets) we
+# may be building using $(if_changed{,_dep}). As an optimization, we
+# don't need to read them if the target does not exist; we will rebuild
+# anyway in that case.
+
+targets := $(wildcard $(sort $(targets)))
+cmd_files := $(wildcard $(foreach f,$(targets),$(dir $(f)).$(notdir $(f)).cmd))
+
+ifneq ($(cmd_files),)
+  include $(cmd_files)
+endif