make FS.ErrnoError inherit from Error
Add return value to sendmsg.
Test for webrtc sockets.
Minor fixes for webrtc test.
Merge pull request #1513 from modeswitch/webrtc-tests

Webrtc test
spam abort() messages to stderr as well
assert in btest on successful compilation
make legacy gl emulation an opt-in option, LEGACY_GL_EMULATION
move shader compile status check behind GL_DEBUG
expose setCanvasSize
Merge pull request #1526 from inolen/glcompileshader

don't check COMPILE_STATUS in glCompileShader by default
make find_bigfuncs work on ll and js
Merge pull request #1527 from inolen/setcanvassize

export setCanvasSize to Module object
Merge pull request #1511 from inolen/errnoerror

make FS.ErrnoError inherit from Error
Add compat headers, move some things to them.

This is groundwork for landing musl includes which remove
some of the deprecated functions or very old BSDisms.
Fix test runner process exit code to report the number of failing tests, like it did before.
convert gl emulation compilation errors to warnings and runtime errors
pick up function indexing that only happens in pre
simplify and automate GetProcAddress logic, and move it out of GL emulation
do not warn on gl emulation code if INCLUDE_FULL_LIBRARY is set, only error at runtime