[source] build: new fixes for symlinked .config handling

[LEDE Commits]

jow pushed a commit to source.git, branch lede-17.01:
https://git.lede-project.org/bb9eb2c96e47b2ca6c3596cf9af1a497d3f55f23

commit bb9eb2c96e47b2ca6c3596cf9af1a497d3f55f23
Author: Sergey Ryazanov <ryazanov.s.a at gmail.com>
AuthorDate: Sun May 7 20:19:13 2017 +0300

    build: new fixes for symlinked .config handling
    
    When running "make {config|defconfig|oldconfig}" with symlinked .config
    (e.g. to env/.config) it renames symlink to .config.old, creates new
    .config file, and writes the updated configuration into it.
    
    This breaks the desired workflow when changes in the configuration can
    be checked using "scripts/env diff" and commited using "scripts/env
    save". Since the env/.config file is not updated.
    
    The things become even worse when working with feeds, since feeds script
    quite often silently invokes "make {oldconfig|defconfig}" and breaks the
    symlink.
    
    Fix this issue by exporting KCONFIG_OVERWRITECONFIG=1, which forces
    mconf to overwrite the .config content, instead of renaming it and
    creating a new file. This variable is set only if .config is a symlink,
    otherwise the variable is not exported and the old behaviour is
    preserved.
    
    This change uses the same behaviour as "make menucofig", which has
    already been fixed in commit 5bf98b1acc3b6b178f8954c5075a58e1e6a99d6a.
    
    Also make a tiny cosmetic update to the "make menuconfig" target code
    layout to make it look like other config handling targets.
    
    Signed-off-by: Sergey Ryazanov <ryazanov.s.a at gmail.com>
    (cherry picked from commit e06d8f0f6f041c8ac1acba810eea96c32dc983e4)
---
 include/toplevel.mk | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/toplevel.mk b/include/toplevel.mk
index 8f967bd..f7c0dc1 100644
--- a/include/toplevel.mk
+++ b/include/toplevel.mk
@@ -105,7 +105,8 @@ scripts/config/conf:
 	@$(_SINGLE)$(SUBMAKE) -s -C scripts/config conf CC="$(HOSTCC_WRAPPER)"
 
 config: scripts/config/conf prepare-tmpinfo FORCE
-	$< Config.in
+	[ -L .config ] && export KCONFIG_OVERWRITECONFIG=1; \
+		$< Config.in
 
 config-clean: FORCE
 	$(_SINGLE)$(NO_TRACE_MAKE) -C scripts/config clean
@@ -113,7 +114,8 @@ config-clean: FORCE
 defconfig: scripts/config/conf prepare-tmpinfo FORCE
 	touch .config
 	@if [ ! -s .config -a -e $(HOME)/.openwrt/defconfig ]; then cp $(HOME)/.openwrt/defconfig .config; fi
-	$< --defconfig=.config Config.in
+	[ -L .config ] && export KCONFIG_OVERWRITECONFIG=1; \
+		$< --defconfig=.config Config.in
 
 confdefault-y=allyes
 confdefault-m=allmod
@@ -121,13 +123,15 @@ confdefault-n=allno
 confdefault:=$(confdefault-$(CONFDEFAULT))
 
 oldconfig: scripts/config/conf prepare-tmpinfo FORCE
-	$< --$(if $(confdefault),$(confdefault),old)config Config.in
+	[ -L .config ] && export KCONFIG_OVERWRITECONFIG=1; \
+		$< --$(if $(confdefault),$(confdefault),old)config Config.in
 
 menuconfig: scripts/config/mconf prepare-tmpinfo FORCE
 	if [ \! -e .config -a -e $(HOME)/.openwrt/defconfig ]; then \
 		cp $(HOME)/.openwrt/defconfig .config; \
 	fi
-	[ -L .config ] && export KCONFIG_OVERWRITECONFIG=1; $< Config.in
+	[ -L .config ] && export KCONFIG_OVERWRITECONFIG=1; \
+		$< Config.in
 
 prepare_kernel_conf: .config FORCE