Support deps files with no output

AIDL generates a deps file with no output listed temporarily pass it
through without error in the makedeps parser.

Bug: 141372861
Test: m checkbuild
Change-Id: I8c6740833dbc2ff3318dfc424ec497728cfc48d2
diff --git a/makedeps/deps.go b/makedeps/deps.go
index e64e6f7..db49532 100644
--- a/makedeps/deps.go
+++ b/makedeps/deps.go
@@ -57,10 +57,12 @@
 				return nil, fmt.Errorf("%sunsupported variable expansion: %v", pos(node), x.Target.Dump())
 			}
 			outputs := x.Target.Words()
-			if len(outputs) == 0 {
-				return nil, fmt.Errorf("%smissing output: %v", pos(node), x)
+			if len(outputs) > 0 {
+				ret.Output = outputs[0].Value(nil)
+			} else {
+				// TODO(b/141372861): put this back
+				//return nil, fmt.Errorf("%smissing output: %v", pos(node), x)
 			}
-			ret.Output = outputs[0].Value(nil)
 
 			if !x.Prerequisites.Const() {
 				return nil, fmt.Errorf("%sunsupported variable expansion: %v", pos(node), x.Prerequisites.Dump())