return 0 on fread on invalid stream
fix file preloading in workers and add test
report better error in fread on bad stream
use externs for fastcomp vars and declare for fastcomp funcs
move import in cache.py to avoid module interdependencies; fallout from 0f5135e436 breaking test_llvm_nativizer
be sure to not emit an external ref as both a var and a func in fastcomp
Fixed glSampleCoverage signature (vi to vii)

The signature for glSampleCoverage was incorrect (vi); glSampleCoverage takes two arguments (vii).

See: https://www.khronos.org/registry/webgl/specs/1.0.2/#5.14.3
and http://www.khronos.org/opengles/sdk/docs/man/xhtml/glSampleCoverage.xml
[SDL Audio] Refactoring Mix_LoadWAV_RW to use new FS API.

The old API was causing issues with certain file systems, as the `read` property required the execute bit AND the read bit to be set before it would return `true`.

As a side benefit, the new code is simpler and cleaner.
Merge pull request #1891 from onnoj/incoming

Fixed glSampleCoverage signature (vi to vii)
do not assume fastcomp emits 'pre' table
finalize function table masks for fastcomp
handle global initializers from fastcomp
shorten test_cubescript for fastcomp now that it passes
fix memset return value in makeSetValues
Merge pull request #1894 from jvilk/legacy_fs_remove

[SDL Audio] Refactoring Mix_LoadWAV_RW to use new FS API.
handle return values for library calls using aliases with different return types
fix creation of temp dir in EMCC_DEBUG for the first time