[Buildroot] [PATCH 3 of 4] manual generation: check dependencies first

[Thomas De Schampheleire <patrickdepinguin@gmail.com>]

To generate the manual, you need asciidoc and w3m. If these are not present,
pretty cryptic error messages are given.
This patch adds a simple check for these dependencies, before attempting to
build the manual.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>

---
 docs/manual/manual.mk |  11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/docs/manual/manual.mk b/docs/manual/manual.mk
--- a/docs/manual/manual.mk
+++ b/docs/manual/manual.mk
@@ -3,6 +3,16 @@ manual-update-lists:
 	$(Q)BR2_DEFCONFIG="" TOPDIR=$(TOPDIR) O=$(O)/docs/manual/.build \
 		$(TOPDIR)/support/scripts/gen-manual-lists.py
 
+manual-check-dependencies:
+	$(Q)if [ -z "`which a2x 2>/dev/null`" ]; then \
+		echo "You need asciidoc on your host to generate the manual"; \
+		false; \
+	fi
+	$(Q)if [ -z "`which w3m 2>/dev/null`" ]; then \
+		echo "You need w3m on your host to generate the manual"; \
+		false; \
+	fi
+
 ################################################################################
 # GENDOC -- generates the make targets needed to build a specific type of
 #           asciidoc documentation.
@@ -24,6 +34,7 @@ define GENDOC_INNER
 
 $$(O)/docs/$(1)/$(1).$(4): docs/$(1)/$(1).txt \
 			   $$($(call UPPERCASE,$(1))_SOURCES) \
+			   manual-check-dependencies \
 			   manual-update-lists
 	$(Q)$(call MESSAGE,"Generating $(5) $(1)...")
 	$(Q)mkdir -p $$(@D)/.build