Added test which shows broken GL emulation when:
1. Binding to a VertexObjectBuffer and calling `glDrawArrays` on two
   different sections of it.
2. Using `glVertexPointer` with actual pointer to a vertex array
   and calling `glDrawArrays` on two different sections of it.
Merge branch 'vertex_array_object_bug' of github.com:michaeljbishop/emscripten into incoming
fix repeated calls to glDraw* where the count changes but not the client attributes; fixes part of #1589
handle glBufferData usages that are not in WebGL; fixes #1589
do not fail in test_dlfcn_qsort of js engine cannot do asm validation; fixes #1591
do not emit externals in side modules
remove no longer needed library.js constants for some libcxxabi stuff, which can confuse INCLUDE_FULL_LIBRARY+exceptions
dlopen+exceptions+asm is not supported yet
longjmp test across asm modules
Merge pull request #1582 from waywardmonkeys/simplify-timezone

Simplify timezone
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 time tests.
Add __va_copy as a compat/stdarg.h
Fix fpclassify with musl libc headers.

musl defines __fpclassify, __fpclassifyf, __fpclassifyl while
the old headers used __fpclassifyd for double rather than
__fpclassify.
Fix seekdir() for 64-bit off_t.
Fix ftello() for 64 bit off_t return value.