manual generation: check dependencies first

To generate the manual, you need a few tools. 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>
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

support/dependencies/check-host-asciidoc.sh

@@ -0,0 +1,36 @@
+#!/bin/sh
+
+candidate="$1" #ignored
+
+asciidoc=`which asciidoc`
+if [ ! -x "$asciidoc" ]; then
+	# echo nothing: no suitable asciidoc found
+	exit 1
+fi
+
+# Output of 'asciidoc --version' examples:
+# asciidoc 8.6.7
+version=`$asciidoc --version | cut -d\  -f2`
+major=`echo "$version" | cut -d. -f1`
+minor=`echo "$version" | cut -d. -f2`
+bugfix=`echo "$version" | cut -d. -f3`
+
+# To generate the manual, we need asciidoc >= 8.6.3
+major_min=8
+minor_min=6
+bugfix_min=3
+if [ $major -gt $major_min ]; then
+	echo $asciidoc
+else
+	if [ $major -eq $major_min -a $minor -ge $minor_min ]; then
+		echo $asciidoc
+	else
+		if [ $major -eq $major_min -a $minor -eq $minor_min \
+			-a $bugfix -ge $bugfix_min ]; then
+			echo $asciidoc
+		else
+			# echo nothing: no suitable asciidoc found
+			exit 1
+		fi
+	fi
+fi