Fix awk(1) limitation.

--- src2man.orig	Thu Mar 17 00:01:38 2011
+++ src2man	Wed Mar 25 10:43:25 2015
@@ -100,7 +100,7 @@ date=${date:-$(date +'%d %B %Y')}
 # Extract manpages from source files. Man page content is enclosed in
 # commment blocks starting by "/** sectnum"
 #
-awk -v release="$release" -v volume="$volume" -v nogen=$nogen '
+gawk -v release="$release" -v volume="$volume" -v nogen=$nogen '
 $1 == "/**" && $2 ~ /^[0-9]/ {
 	sect = $2
 	getline