web-wasi-emulated-threads: initial addition

Todos:

- Add to CI if possible (builds LLVM/Clang)
- Add to README

web-wasi-emulated-threads/FindOpenGL.cmake

@@ -0,0 +1,34 @@
+# Locate OpenGL
+# This module defines:
+# OPENGL_FOUND       - system has OpenGL
+# OPENGL_XMESA_FOUND - system has XMESA
+# OPENGL_GLU_FOUND   - system has GLU
+# OPENGL_INCLUDE_DIR - the GL include directory
+# OPENGL_LIBRARIES   - Link these to use OpenGL and GLU
+# OPENGL_gl_LIBRARY  - Path to OpenGL Library
+# OPENGL_glu_LIBRARY - Path to GLU Library
+
+# The implementation is based on the standard FindOpenGL.cmake provided with CMake,
+# but customized for targeting Emscripten only.
+
+# These libraries are provided with Emscripten
+SET(OPENGL_FOUND TRUE)
+SET(OPENGL_GLU_FOUND TRUE)
+
+# Doesn't look like this one is part of Emscripten
+SET(OPENGL_XMESA_FOUND FALSE)
+
+# This is the path where <GL/gl.h> is found
+SET(OPENGL_INCLUDE_DIR "${EMSCRIPTEN_ROOT_PATH}/system/include")
+
+# No library to link against for OpenGL, since Emscripten picks it up automatically from library_webgl.js,
+# but need to report something, or CMake thinks we failed in the search.
+SET(OPENGL_LIBRARIES "nul")
+SET(OPENGL_gl_LIBRARY "nul")
+SET(OPENGL_glu_LIBRARY "nul")
+
+mark_as_advanced(
+  OPENGL_INCLUDE_DIR
+  OPENGL_glu_LIBRARY
+  OPENGL_gl_LIBRARY
+)