configure: allow enabling unit tests

configure

@@ -58,6 +58,7 @@ gen_CFLAGS () {
 			 dmd) cflags="$cflags -debug";;
 		esac
 	fi
+	[ -n "$unittest" ] && cflags="$cflags -unittest -main"
 
 	for flag in $cflags; do
 		using "$flag"
@@ -85,7 +86,7 @@ gen_LDFLAGS () {
 
 # command line interface
 
-while getopts c:dhr ch; do
+while getopts c:dhrt ch; do
 	case "$ch" in
 		c)
 			dcname="$(basename "$OPTARG")"
@@ -97,6 +98,7 @@ while getopts c:dhr ch; do
 			;;
 		d) debug=1 ;;
 		r) unset debug ;;
+		t) unittest=1; debug=1 ;;
 		h)
 			cat <<EOF
 configure: create an optimised makefile for the current environment
@@ -105,6 +107,7 @@ options:
   -c: force use of a particular compiler (dmd or ldc2)
   -d: build in debug mode, with debug symbols and statements enabled
   -r: build in release mode with optimisation flags enabled (default)
+  -t: build an executable to run unit tests (implies -d)
   -h: show this help message
 EOF
 			exit 0