godot: Compiling with Javascript tools=yes fails (no exceptions support for Clipper and Assimp build)

Godot version: master (https://github.com/godotengine/godot/commit/2c9536b655d006c697a3cf830ad3352f1a1ed9f2)

OS/device including version: Arch Linux

Issue description: The javascript export (html5) fails with tools=yes. I think it should work because there was the website http://godot.online.

[ 72%] Compiling ==> editor/collada/collada.cpp
thirdparty/misc/clipper.cpp:901:7: error: cannot use 'throw' with exceptions
      disabled
      throw clipperException("Coordinate outside allowed range");
      ^
thirdparty/misc/clipper.cpp:1049:5: error: cannot use 'throw' with exceptions
      disabled
    throw clipperException("AddPath: Open paths must be subject.");
    ^
thirdparty/misc/clipper.cpp:1081:5: error: cannot use 'throw' with exceptions
      disabled
    throw; //range test fails
    ^
thirdparty/misc/clipper.cpp:1065:3: error: cannot use 'try' with exceptions
      disabled
  try
  ^
thirdparty/misc/clipper.cpp:1445:5: error: cannot use 'throw' with exceptions
      disabled
    throw clipperException("UpdateEdgeIntoAEL: invalid call");
    ^
thirdparty/misc/clipper.cpp:1513:5: error: cannot use 'throw' with exceptions
      disabled
    throw clipperException("Error: PolyTree struct is needed for open pa...
    ^
thirdparty/misc/clipper.cpp:1563:3: error: cannot use 'try' with exceptions
      disabled
  try {
  ^
thirdparty/misc/clipper.cpp:2841:5: error: cannot use 'throw' with exceptions
      disabled
    throw clipperException("ProcessIntersections error");
    ^
thirdparty/misc/clipper.cpp:2830:3: error: cannot use 'try' with exceptions
      disabled
  try {
  ^
thirdparty/misc/clipper.cpp:3005:8: error: cannot use 'throw' with exceptions
      disabled
  else throw clipperException("DoMaxima error");
       ^
10 errors generated.
shared:ERROR: compiler frontend failed to generate LLVM bitcode, halting
scons: *** [thirdparty/misc/clipper.javascript.opt.tools.64.bc] Error 1
scons: building terminated because of errors.

Steps to reproduce: scons p=javascript tools=yes target=release_debug bits=64 -j 8