Makefile: split off 'list-defconfigs' from 'help'

As discussed in the FOSDEM2015 BR developer meeting, the output of
'make help' is too long for comfortable reading. To shorten it, split
off the list of defconfigs in a new target, 'list-defconfigs'.

Declare the new target as phony.

Add 'list-defconfigs' to the documentation.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Makefile

@@ -435,7 +435,7 @@ world: target-post-image
 
 .PHONY: all world toolchain dirs clean distclean source outputmakefile \
 	legal-info legal-info-prepare legal-info-clean printvars help \
-	target-finalize target-post-image \
+	list-defconfigs target-finalize target-post-image \
 	$(TARGETS) $(TARGETS_ROOTFS) \
 	$(TARGETS_DIRCLEAN) $(TARGETS_SOURCE) $(TARGETS_LEGAL_INFO) \
 	$(BUILD_DIR) $(STAGING_DIR) $(TARGET_DIR) \
@@ -907,6 +907,11 @@ endif
 	@echo '  make V=0|1             - 0 => quiet build (default), 1 => verbose build'
 	@echo '  make O=dir             - Locate all output files in "dir", including .config'
 	@echo
+	@echo 'For further details, see README, generate the Buildroot manual, or consult'
+	@echo 'it on-line at http://buildroot.org/docs.html'
+	@echo
+
+list-defconfigs:
 	@echo 'Built-in configs:'
 	@$(foreach b, $(sort $(notdir $(wildcard $(TOPDIR)/configs/*_defconfig))), \
 	  printf "  %-35s - Build for %s\\n" $(b) $(b:_defconfig=);)
@@ -917,9 +922,6 @@ ifneq ($(wildcard $(BR2_EXTERNAL)/configs/*_defconfig),)
 	  printf "  %-35s - Build for %s\\n" $(b) $(b:_defconfig=);)
 endif
 	@echo
-	@echo 'For further details, see README, generate the Buildroot manual, or consult'
-	@echo 'it on-line at http://buildroot.org/docs.html'
-	@echo
 
 release: OUT = buildroot-$(BR2_VERSION)
 

docs/manual/customize-outside-br.txt

@@ -100,6 +100,6 @@ And then in +$(BR2_EXTERNAL)/package/package1+ and
 
  * One can store Buildroot defconfigs in the +configs+ subdirectory of
    +$(BR2_EXTERNAL)+. Buildroot will automatically show them in the
-   output of +make help+ and allow them to be loaded with the normal
-   +make <name>_defconfig+ command. They will be visible under the
-   +User-provided configs+' label in the 'make help' output.
+   output of +make list-defconfigs+ and allow them to be loaded with the
+   normal +make <name>_defconfig+ command. They will be visible under the
+   +User-provided configs+' label in the 'make list-defconfigs' output.

docs/manual/make-tips.txt

@@ -12,6 +12,12 @@ This is a collection of tips that help you make the most of Buildroot.
  $ make V=1 <target>
 --------------------
 
+.Display the list of boards with a defconfig:
+
+--------------------
+ $ make list-defconfigs
+--------------------
+
 .Display all available targets:
 
 --------------------