more docs for outlining
improve test_html_source_map
make script tag async in shell.html
Merge pull request #1551 from waywardmonkeys/fix_browser_test_issues

Fix browser test issues
settings.js docs
Update libc headers to use musl headers.
Fixup libcxx to work with musl includes.
Fix test_zlib. off_t is now 64bit.
Update to work with new libc headers.
Fix other.test_embind & other.test_static_link.
Fix test_time.
Add __va_copy as a compat/stdarg.h