Issues with examples on Windows

The threads example shows a plain white window and then exits with

(exit code: 0xc0000005, STATUS_ACCESS_VIOLATION)

The offscreen example panics with

thread 'main' panicked at 'gl function was not loaded', D:\personal\software\contribution\surfman\target\debug\build\gl-76f8da451bedeb81\out/bindings.rs:20624:13
stack backtrace:
   0: backtrace::backtrace::trace_unsynchronized
             at C:\Users\VssAdministrator\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.40\src\backtrace\mod.rs:66
   1: std::sys_common::backtrace::_print_fmt
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\sys_common\backtrace.rs:77
   2: std::sys_common::backtrace::_print::{{impl}}::fmt
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\sys_common\backtrace.rs:59
   3: core::fmt::write
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libcore\fmt\mod.rs:1052
   4: std::io::Write::write_fmt<std::sys::windows::stdio::Stderr>
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\io\mod.rs:1426
   5: std::sys_common::backtrace::_print
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\sys_common\backtrace.rs:62
   6: std::sys_common::backtrace::print
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\sys_common\backtrace.rs:49
   7: std::panicking::default_hook::{{closure}}
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\panicking.rs:204
   8: std::panicking::default_hook
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\panicking.rs:224
   9: std::panicking::rust_panic_with_hook
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\panicking.rs:472
  10: std::panicking::begin_panic<str*>
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\src\libstd\panicking.rs:399
  11: gl::missing_fn_panic
             at D:\personal\software\contribution\surfman\target\debug\build\gl-76f8da451bedeb81\out\bindings.rs:20624
  12: gl::CreateShader
             at D:\personal\software\contribution\surfman\target\debug\build\gl-76f8da451bedeb81\out\bindings.rs:1736
  13: offscreen::common::Shader::new
             at .\examples\common\mod.rs:57
  14: offscreen::TriProgram::new
             at .\examples\offscreen.rs:168
  15: offscreen::TriVertexArray::new
             at .\examples\offscreen.rs:129
  16: offscreen::main
             at .\examples\offscreen.rs:88
  17: std::rt::lang_start::{{closure}}<()>
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\src\libstd\rt.rs:67
  18: std::rt::lang_start_internal::{{closure}}
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\rt.rs:52
  19: std::panicking::try::do_call<closure-0,i32>
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\panicking.rs:305
  20: panic_unwind::__rust_maybe_catch_panic
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libpanic_unwind\lib.rs:86
  21: std::panicking::try
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\panicking.rs:281
  22: std::panic::catch_unwind
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\panic.rs:394
  23: std::rt::lang_start_internal
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\/src\libstd\rt.rs:51
  24: std::rt::lang_start<()>
             at /rustc/b8cedc00407a4c56a3bda1ed605c6fc166655447\src\libstd\rt.rs:67
  25: main
  26: invoke_main
             at d:\agent\_work\2\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:78
  27: __scrt_common_main_seh
             at d:\agent\_work\2\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288
  28: BaseThreadInitThunk
  29: RtlUserThreadStart

Reproduce the threads and offscreen examples on Windows, then inspect examples/common/mod.rs and examples/offscreen.rs, including the reported Shader::new and TriProgram::new locations. Trace why the OpenGL function is unavailable and why the threads example exits with an access violation; done means both examples run without these failures.