Add to suite of MSL tests and references any existing GLSL tests
that successfully convert GLSL->SPIRV->MSL and compile as MSL.
test_shaders_helper() ignores hidden files that start with '.',
to avoid accidentally finding hidden OSX files such as .DS_Store.
Use xcrun to compile MSL shaders instead of hard-coded path to Metal compiler.
Wrap calls to xcrun in exception handling to ignore if Xcode not installed.
For MSL tests, move call to validate_shader_msl() to after call to
regression_check() to allow a converted MSL shader to be saved for
manual review even if it doesn't successfully compile as MSL.
This helps pinpoint the issues due to differences in the Metal compiler
version and also indicates whether we are actually using the compiler to
validate MSL output.
If we run on a system with Xcode installed to a default path, run Xcode
Metal shader compiler to validate the generated MSL shader.
This uncovers an issue in the existing MSL test - MSL backend currently
does not auto-assign attribute locations, which means that translating
GLSL shader without location layout produces an invalid MSL which
generates "error: 'attribute' index '0' is used more than once".
To extract a column from row-major matrix, we need to do a strided load one
component at a time. In this case flattened_access_chain_offset still returns
the offset to the first element, but the stride is equal to matrix stride
instead of vector stride.
For this to work, we need to pass matrix stride (and transpose flag) through,
similar to how matrix flattening works.
Additionally slightly clean up recursive flattened_access_chain structure -
specifically, instead of deciding mid-traversal that we need matrix stride
information, we can just pass the matrix stride through - for access chains
that end in matrix/vector this gets us what we need, and for access chains
that end in structs the flattened_access_chain_struct code will recompute
correct stride/transposition data to pass through further.
