layers:Remove includes of vk_safe_struct.cpp

[tobine]

After looking at these includes of vk_safe_struct.cpp I believe it was
just a hack that worked and has persisted in the code. This change
pulls the source into the layers that depend on it at build time and is
a better solution, in my opinion.

The one quirk is that the we now generate vk_struct.cpp in the base dir
and in the layers dir. Since the file is required by some layer shared
libs I had to generate in the layers dir, but there are also some
dependencies on the file in the top-level dir that I didn't care to
investigate further so I just genrate it in two places.
I'm sure this could be cleaned up if someone with more cmake knowledge
and/or patience than me cares to look into it further.

[chrisforbes]

This looks like it's getting there (finally clean on travis!).

[chrisforbes]

Don't much like .cpp files in include/

[tobine]

I updated android codegen to put vk_safe_struct.cpp into "common" dir instead of "include" and use it from there in layer libs.

[stroyan]

Unfortunately, the weird use of include for vk_safe_struct.cpp is still required to prevent visual studio from doing conflict file generation during parallel builds.
Perhaps the file should be changed to a generated .h header to match the way it is used.

[chrisforbes]

@stroyan or we can move this down a level into a static lib, and have the layers depend on that?

[mark-lunarg]

@stroyan, any reply to @chrisforbes?

[mark-lunarg]

@tobine, @stroyan, any update here, or can we just get by with things the way they are now?

[stroyan]

It would be nice to get back to using a proper add_library rule for using vk_safe_struct.cpp.
Looking at the current https://cmake.org/Wiki/CMake_FAQ description of this problem I see
that there is an alternative workaround of making one of the layers depend on the other.
Then the two layers that use vk_safe_struct.cpp will not be built in parallel.
Then visual studio will never clobber vk_safe_struct.cpp.
That could be accomplished by adding one more rule to layers/CMakeLists.txt in the section
starting with- # Core validation has additional dependencies
Add-

# Dependency on unique_objects is only to prevent parallel build of both layers.
# Visual Studio has trouble with clobbering vk_safe_struct.cpp if both build in parallel.
add_dependencies(VkLayer_core_validation VkLayer_unique_objects)

I don't have a system available right now to confirm if visual studio does the right thing with that additional rule.

[tobine]

Updated with WA suggested by @stroyan and re-testing.

[mark-lunarg]

@tobine, this repository will close for write access on Sunday, 5/13/2018. If it is pushed before that time it will be present in the follow-on Vulkan-ValidationLayers repository on Monday, otherwise a new PR will be required in the new repo.