asmjs: can not ignore errors on missing libraries

The current Emscripten release is not happy with the use of
"-s ERROR_ON_MISSING_LIBRARIES=0" as a link option, it gives an error
stating that all libraries must now be present, so remove that use.

This leaves a missing 'util' library. This did not appear to be
needed on the few builds I have tried, and this patch avoids adding
this library for asmjs.

scripts/genie.lua

@@ -1183,7 +1183,6 @@ configuration { "asmjs" }
 	}
 	linkoptions {
 		"-Wl,--start-group",
-		"-s ERROR_ON_MISSING_LIBRARIES=0"
 	}
 	archivesplit_size "20"
 

scripts/src/osd/sdl.lua

@@ -328,7 +328,7 @@ if BASE_TARGETOS=="unix" then
 					"socket",
 					"nsl",
 				}
-			else
+			elseif _OPTIONS["targetos"]~="asmjs" then
 				links {
 					"util",
 				}