[HTML5] Fix build for recent emscripten versions.

Library suffix should be `.a`, the `EXTRA_` in
`EXTRA_EXPORTED_RUNTIME_METHODS` is deprecated.

platform/javascript/detect.py

@@ -172,7 +172,7 @@ def configure(env):
     # Program() output consists of multiple files, so specify suffixes manually at builder.
     env["PROGSUFFIX"] = ""
     env["LIBPREFIX"] = "lib"
-    env["LIBSUFFIX"] = ".bc"
+    env["LIBSUFFIX"] = ".a"
     env["LIBPREFIXES"] = ["$LIBPREFIX"]
     env["LIBSUFFIXES"] = ["$LIBSUFFIX"]
 
@@ -226,8 +226,8 @@ def configure(env):
     # Allow use to take control of swapping WebGL buffers.
     env.Append(LINKFLAGS=["-s", "OFFSCREEN_FRAMEBUFFER=1"])
 
-    # callMain for manual start.
-    env.Append(LINKFLAGS=["-s", "EXTRA_EXPORTED_RUNTIME_METHODS=['callMain','cwrap']"])
+    # callMain for manual start, cwrap for the mono version.
+    env.Append(LINKFLAGS=["-s", "EXPORTED_RUNTIME_METHODS=['callMain','cwrap']"])
 
     # Add code that allow exiting runtime.
     env.Append(LINKFLAGS=["-s", "EXIT_RUNTIME=1"])