The application "Command & Conquer: Rivals" uses the following pattern:

    // Create and link VS, save binary data
    glCreateProgram()
    glAttachShader()
    glLinkProgram()
    glGetProgramBinary()

    // Create and link FS, save binary data
    glCreateProgram()
    glAttachShader()
    glLinkProgram()
    glGetProgramBinary()
    ...
    // Create VS, load binary data
    glCreateProgram()
    glProgramBinary()

    // Create FS, load binary data
    glCreateProgram()
    glProgramBinary()
    ...
    glUseProgramStages(GL_VERTEX_SHADER_BIT)
    glUseProgramStages(GL_FRAGMENT_SHADER_BIT)
    glBindProgramPipeline()

Later, when issuing the draw command that uses the PPO, the PPO must be
linked with the Programs that were loaded via binary data. Those
Programs don't have any Shaders attached, just linked. This CL adds
support for linking Programs without attached Shaders.

Bug: b/182409935
Test: ProgramPipelineTest31.ProgramBinary
Change-Id: Ic5a4776e1374322665f45fbbcbf955838d093d02
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2770685
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>