wasm: enable exception support for exprtk

- `TestGlyph3DMapperOrientationArray` uses vtkArrayCalculator
which internally uses exprtk. This test threw an uncaught exception
from exprtk because in wasm, exceptions are not enabled by default.
- This commit enables exception support when compiling the exprtk
library with emscripten. The exception support is not enabled
for all targets yet because the emscripten docs say this flag
has a large overhead in performance.