scripts/gdb: delay generation of gdb constants.py

scripts/gdb/linux/constants.py is never used in the kernel build
process. There is no good reason to create it so early.

Get it out of the 'prepare' stage.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

Kbuild

@@ -6,7 +6,6 @@
 # 2) Generate timeconst.h
 # 3) Generate asm-offsets.h (may need bounds.h and timeconst.h)
 # 4) Check for missing system calls
-# 5) Generate constants.py (may need bounds.h)
 
 #####
 # 1) Generate bounds.h
@@ -58,14 +57,5 @@ quiet_cmd_syscalls = CALL    $<
 missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE
 	$(call cmd,syscalls)
 
-#####
-# 5) Generate constants for Python GDB integration
-#
-
-extra-$(CONFIG_GDB_SCRIPTS) += build_constants_py
-
-build_constants_py: $(timeconst-file) $(bounds-file)
-	@$(MAKE) $(build)=scripts/gdb/linux $@
-
 # Keep these three files during make clean
 no-clean-files := $(bounds-file) $(offsets-file) $(timeconst-file)

Makefile

@@ -1519,6 +1519,17 @@ PHONY += $(DOC_TARGETS)
 $(DOC_TARGETS): scripts_basic FORCE
 	$(Q)$(MAKE) $(build)=Documentation $@
 
+# Misc
+# ---------------------------------------------------------------------------
+
+PHONY += scripts_gdb
+scripts_gdb: prepare
+	$(Q)$(MAKE) $(build)=scripts/gdb/linux build_constants_py
+
+ifdef CONFIG_GDB_SCRIPTS
+all: scripts_gdb
+endif
+
 else # KBUILD_EXTMOD
 
 ###