Support BuiltInFragDepth.
Emit interface block for StorageClassUniformConstant.
Throw exception when output or fragment input structs contain matrix or array.
Dynamically created interface structs sorted by location number instead of alphabetically.
Add Compiler::is_array() function.
CompilerMSL accesses options using same design pattern as CompilerGLSL and CompilerHLSL.
CompilerMSL support setting VA & rez binding specs via either constructor or compile() method overload.
CompilerMSL support single UBO packing and padding in single pass.
spriv_cross app (main.cpp) supports turning off UBO packing and padding via command line option.
Add MSL UBO alignment test shader.
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.
