If required modules are not available (e.g. in a browser), we fall back
to console.log().

This also allows us to pass fixedbugs/issue22326.go test in Go 1.16.

These tests cover nuances of interaction between unsafe and GC, which
are not applicable to the JavaScript runtime.

Note: fixedbugs/issue24491a.go seems to panic where I don't think it
should, is likely related to issue gopherjs#1001.

These tests rely on features GopherJS currently doesn't support.

Upon a cursory look, the test seems to panic when it is expected to, but
the panic message is formatted differently, hence the test failure.

This mirrors the upstream golang/go#31546 and
allows `fixedbugs/issue31546.go` to pass.

This test manifested a different issue in GopherJS compiler, which
requires more research than I currently have time for. See
gopherjs#1007 for details.

Tests use an unsupported compiler flag and target aspects of `unsafe`
package GopherJS doesn't support.

This addresses the point of the test, but we still have to skip it
because printed output is formatted slightly differently.

$callDeferred() uses `throw null` to interrupt normal execution when
called from a panic(). However, it simply returns when called orderly
at the end of a function.

A tricky interaction may happen when one of the deferred function blocks
on a channel or mutex. The goroutine will get paused and when it
unblocks, deferrals will continue to execute via $callDeferred() at the
end of the function. Under that circumstance `throw null` trick is
unnecessary since the main body of the function is outside of the call
stack anyway.

This fix allows fixedbugs/issue40629.go test to pass successfully.

3f703aa enabled source map support in the CI, so this test is now able
to pass.

These tests take quite a while to complete, so build able to focus on
our own tests is a time saver during development.