btrfs-progs: autogen: add check for pkg-config

Configure uses pkg-config, this should be at least checked at the
autogen time.

Signed-off-by: David Sterba <dsterba@suse.com>

autogen.sh

@@ -41,6 +41,15 @@ test -f btrfs.c || {
 	DIE=1
 }
 
+(pkg-config --version) < /dev/null > /dev/null 2>&1 || {
+	echo
+	echo "You must have pkg-config installed to use btrfs-progs build system."
+	echo "The pkg-config utility was not found in the standard location, set"
+	echo "the PKG_CONFIG/PKG_CONFIG_PATH/PKG_CONFIG_LIBDIR variables at the"
+	echo "configure time."
+	echo
+}
+
 if test "$DIE" -eq 1; then
 	exit 1
 fi