[HTML5] Reorganize build script.

Simplify helper functions, fix env/sys_env confusion and depends for
externs and pre-js.

platform/javascript/SCsub

@@ -27,8 +27,13 @@ if env["tools"]:
     sys_env.AddJSLibraries(["js/libs/library_godot_editor_tools.js"])
 if env["javascript_eval"]:
     sys_env.AddJSLibraries(["js/libs/library_godot_eval.js"])
+
 for lib in sys_env["JS_LIBS"]:
     sys_env.Append(LINKFLAGS=["--js-library", lib])
+for js in env["JS_PRE"]:
+    sys_env.Append(LINKFLAGS=["--pre-js", env.File(js).path])
+for ext in env["JS_EXTERNS"]:
+    sys_env["ENV"]["EMCC_CLOSURE_ARGS"] += " --externs " + ext.path
 
 build = []
 if env["gdnative_enabled"]:
@@ -66,16 +71,8 @@ else:
     build = sys_env.Program(build_targets, javascript_files + ["javascript_runtime.cpp"])
 
 sys_env.Depends(build[0], sys_env["JS_LIBS"])
-
-if "JS_PRE" in env:
-    for js in env["JS_PRE"]:
-        env.Append(LINKFLAGS=["--pre-js", env.File(js).path])
-    env.Depends(build, env["JS_PRE"])
-
-if "JS_EXTERNS" in env:
-    for ext in env["JS_EXTERNS"]:
-        env["ENV"]["EMCC_CLOSURE_ARGS"] += " --externs " + ext.path
-    env.Depends(build, env["JS_EXTERNS"])
+sys_env.Depends(build[0], sys_env["JS_PRE"])
+sys_env.Depends(build[0], sys_env["JS_EXTERNS"])
 
 engine = [
     "js/engine/preloader.js",

platform/javascript/detect.py

@@ -131,7 +131,10 @@ def configure(env):
         jscc = env.Builder(generator=run_closure_compiler, suffix=".cc.js", src_suffix=".js")
         env.Append(BUILDERS={"BuildJS": jscc})
 
-    # Add helper method for adding libraries.
+    # Add helper method for adding libraries, externs, pre-js.
+    env["JS_LIBS"] = []
+    env["JS_PRE"] = []
+    env["JS_EXTERNS"] = []
     env.AddMethod(add_js_libraries, "AddJSLibraries")
     env.AddMethod(add_js_pre, "AddJSPre")
     env.AddMethod(add_js_externs, "AddJSExterns")

platform/javascript/emscripten_helpers.py

@@ -22,18 +22,12 @@ def create_engine_file(env, target, source, externs):
 
 
 def add_js_libraries(env, libraries):
-    if "JS_LIBS" not in env:
-        env["JS_LIBS"] = []
     env.Append(JS_LIBS=env.File(libraries))
 
 
 def add_js_pre(env, js_pre):
-    if "JS_PRE" not in env:
-        env["JS_PRE"] = []
     env.Append(JS_PRE=env.File(js_pre))
 
 
 def add_js_externs(env, externs):
-    if "JS_EXTERNS" not in env:
-        env["JS_EXTERNS"] = []
     env.Append(JS_EXTERNS=env.File(externs))