modpost: re-add -e to set external_module flag

Previously, the -i option had two functions; load a symbol dump file,
and set the external_module flag.

I want to assign a dedicate option for each of them.

Going forward, the -i is used to load a symbol dump file, and the -e
to set the external_module flag.

With this, we will be able to use -i for loading in-kernel symbols.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/Makefile.modpost

@@ -79,6 +79,10 @@ src := $(obj)
 # Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
 include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
              $(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
+
+# modpost option for external modules
+MODPOST += -e
+
 endif
 
 # modpost options for modules (both in-kernel and external)