Makefile.include: add BUILD_FILES

- Add BULD_FILES that holds all files that need to be built
  and linked.

Makefile.include

@@ -442,6 +442,9 @@ ifeq (,$(FLASHFILE))
   $(error FLASHFILE is not defined for this board: $(FLASHFILE))
 endif
 
+# By default always build ELFFILE and FLASHFILE
+BUILD_FILES += $(ELFFILE) $(FLASHFILE)
+
 # variables used to compile and link c++
 CPPMIX ?= $(if $(wildcard *.cpp),1,)
 
@@ -470,7 +473,7 @@ ifeq ($(BUILD_IN_DOCKER),1)
 link: ..in-docker-container
 else
 ifeq (,$(RIOTNOLINK))
-link: ..compiler-check ..build-message $(ELFFILE) $(FLASHFILE) print-size
+link: ..compiler-check ..build-message $(BUILD_FILES) print-size
 else
 link: ..compiler-check ..build-message $(BASELIBS)
 endif # RIOTNOLINK

makefiles/vars.inc.mk

@@ -80,6 +80,7 @@ export ELFFILE               # The unstripped result of the compilation.
 export HEXFILE               # The 'intel hex' stripped result of the compilation.
 # BINFILE                    # The 'binary' stripped result of the compilation.
 # FLASHFILE                  # The output file used for flashing
+# BUILD_FILES                # The list of files to be built
 # DEBUGGER                   # The command to call on "make debug", usually a script starting the GDB front-end.
 # DEBUGGER_FLAGS             # The parameters to supply to DEBUGGER.
 # DEBUGSERVER                # The command to call on "make debug-server", usually a script starting the GDB server.