Amber ignores name and always uses "main" causing breakage

[seanbaxter]

https://gist.github.com/seanbaxter/c5311a9b7b950fad1d8bade4db395fa0

I took compute_mat2x2.amber from the tests and changed the shader name to "my_shader" now it breaks.

[dj2]

The name in the SHADER line is used to link to the ATTACH command, not the name of the entry point inside the shader. You have to use the ATTACH kVertexShader ENTRY_POINT main version to change the entry point name.