Disable emscripten dynamic execution

[sguimmara]

This PR disables emitting dynamic execution code with Emscripten. This makes it possible to use the laz-perf WASM package in a context where the Content Security Policy (CSP) prohibits running dynamically evaluated code, such as code evaluated by the eval() function, or code passed to the Function constructor.

This is done by passing the -s DYNAMIC_EXECUTION=0 flag in the CMakeLists.txt for Emscripten.

fix #158

[abellgithub]

Are there any downsides to this for people not using this in the context of a browser? Do we care?

[hobu]

No downsides, and this probably should have been the default.

[sguimmara]

Here is the relevant Emscripten doc: https://emscripten.org/docs/tools_reference/settings_reference.html#dynamic-execution

When this flag is set, the following features (linker flags) are unavailable:

   RELOCATABLE: the function loadDynamicLibrary would need to eval().

and some features may fall back to slower code paths when they need to: Embind: uses eval() to jit functions for speed.

In the worst case scenario, we could have 2 different builds, one for the node environment and one for worker/web (currently they all use the exact same generated files). I don't think it's really worth it though.