PIX: stabilize block enumeration order for PIX's instruction numbering pass.

[jeffnn]

PIX has a pass that adds "instruction ordinals" in order to have a common communication mechanism between, e.g., shader debugging instrumentation and the PIX UI. Unfortunately, the enumeration order of basic blocks in a module isn't necessarily stable, resulting in odd things happening in shader debugging. This change attempts to sort basic blocks so that instructions have a consistent ordering.

[AppVeyorBot]

:white_check_mark: Build DirectXShaderCompiler 1.0.1924 completed (commit https://github.com/microsoft/DirectXShaderCompiler/commit/e906e70f7c by @jeffnn)

[jeffnn]

This wasn't really a problem. Abandoning PR.