* Changed unit tests to only record known the validation pass/fail
status
* errors are output as part of the failure message if the result is
unexpected
* can turn off validation for each test individually
* Moved some SPV_KHR_vulkan_memory_model tests to be compiled for Vulkan
1.1
Append() method is special: unlike most outputs, it does not copy
some temporary data to a symbol in the entry point epilogue, but
rather uses an emit builtin after each write to the output stream.
This had been handled by remembering the special output symbol for
the stream as it was declared in the shader entry point before
symbol sanitization. However the prior code was too simple and
only handled cases where the Append() method happened after the
entry point, so that the output symbol had been seen.
This PR adds a patching step so that the Append()s may appear in
any order WRT the entry point. They are patched in an epilogue,
whereupon it is guaranteed in a well formed shader that we have
seen the appropriate declaration.
Fixes#1217.
