[PATCH][4.15?] libxl/ACPI: add missing build dependency

[Jan Beulich <jbeulich@xxxxxxxx>]

Just like all other object files - wherever *.o is mentioned, *.opic
also needs mentioning to yield consistent behavior. Otherwise make may
decide to (re)build the object before recursion into $(ACPI_PATH)/ (to
update $(DSDT_FILES-y) and ssdt_*.h) was actually finished.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
A related but separate issue is that build.o* get rebuilt even if none
of their file dependencies changed, merely - aiui - because of their
dependency on the phony "acpi" target. It may be possible to limit this
rebuilding by making both depend on $(DSDT_FILES-y) instead, but then
they would still get rebuilt for no reason when that file (if any)
changed (but ssdt_*.h didn't).

--- a/tools/libs/light/Makefile
+++ b/tools/libs/light/Makefile
@@ -32,7 +32,7 @@ ACPI_PATH  = $(XEN_ROOT)/tools/libacpi
 DSDT_FILES-$(CONFIG_X86) = dsdt_pvh.c
 ACPI_OBJS  = $(patsubst %.c,%.o,$(DSDT_FILES-y)) build.o static_tables.o
 ACPI_PIC_OBJS = $(patsubst %.o,%.opic,$(ACPI_OBJS))
-$(DSDT_FILES-y) build.o: acpi
+$(DSDT_FILES-y) build.o build.opic: acpi
 vpath build.c $(ACPI_PATH)/
 vpath static_tables.c $(ACPI_PATH)/