[js] respect `-D source-map` flag to generate source maps in release builds

extra/CHANGES.txt

@@ -4,6 +4,7 @@ XXXX-XX-XX: 4.0.0-preview.4
 
 	all : implemented `for` loop unrolling (#3784)
 	js : added externs for js.Date (#6855)
+	js : respect `-D source-map` flag to generate source maps in release builds
 
 	Bugfixes:
 

src/generators/genjs.ml

@@ -1267,7 +1267,7 @@ let set_current_class ctx c =
 
 let alloc_ctx com =
 	let smap =
-		if com.debug || Common.defined com Define.JsSourceMap then
+		if com.debug || Common.defined com Define.JsSourceMap || Common.defined com Define.SourceMap then
 			Some {
 				source_last_pos = { file = 0; line = 0; col = 0};
 				print_comma = false;