The GLES 1.0 headers ANGLE uses are generated using the Khronos tools but modified to include function pointer types and function prototype guards.
Install Python 3 (not 2) with the lxml addon. You can do this using pip install lxml from your Python's Scripts folder.
Edit OpenGL-Registry/xml/genheaders.py:
# GLES 1.x API + mandatory extensions - GLES/gl.h (no function pointers)prefixText = prefixStrings + gles1PlatformStrings + genDateCommentString, to prefixText = prefixStrings + gles1PlatformStrings + apiEntryPrefixStrings + genDateCommentString,genFuncPointers = False, to genFuncPointers = True,protectProto = False, to protectProto = 'nonzero',protectProtoStr = 'GL_GLEXT_PROTOTYPES', to protectProtoStr = 'GL_GLES_PROTOTYPES',Set your working directory to OpenGL-Registry/xml/.
Run python genheaders.py ../api/GLES/gl.h
The generated header will now be in OpenGL-Registry/api/GLES/gl.h. You can copy the header over to this folder.
Also update scripts/gl.xml with the latest version from OpenGL-Registry/xml/.