Add test for --empty-sourcemap

Author: OlivierNicole

compiler/tests-jsoo/empty_sourcemap.t

@@ -0,0 +1,25 @@
+  $ echo 'prerr_endline "a"' > a.ml
+  $ echo 'prerr_endline "b"' > b.ml
+  $ ocamlc -g a.ml -c
+  $ ocamlc -g b.ml -c
+  $ ocamlc -g a.cmo b.cmo -o test.bc
+
+Build object files and executable with --empty-sourcemap:
+
+  $ dune exec -- js_of_ocaml --sourcemap --empty-sourcemap a.cmo -o a.js
+  $ cat a.map
+  {"version":3,"file":"a.js","names":[],"sources":[],"mappings":"","sourcesContent":[]}
+  $ dune exec -- js_of_ocaml --sourcemap --empty-sourcemap b.cmo -o b.js
+  $ cat b.map
+  {"version":3,"file":"b.js","names":[],"sources":[],"mappings":"","sourcesContent":[]}
+  $ dune exec -- js_of_ocaml --sourcemap --empty-sourcemap test.bc -o test.js
+  $ cat test.map
+  {"version":3,"file":"test.js","names":[],"sources":[],"mappings":"","sourcesContent":[]}
+
+Build object files with sourcemap and link with --empty-sourcemap:
+
+  $ dune exec -- js_of_ocaml --sourcemap a.cmo -o a.js
+  $ dune exec -- js_of_ocaml --sourcemap b.cmo -o b.js
+  $ dune exec -- js_of_ocaml link --sourcemap --resolve-sourcemap-url=true --empty-sourcemap a.js b.js -o test.js -a
+  $ cat test.map
+  {"version":3,"file":"test.js","sections":[]}