introducing llvm::trivially_{copy,move}_constructible type traits.
This uses a completely portable implementation of these traits provided
by Richard Smith. You can see it on compiler explorer in all its glory:
https://godbolt.org/g/QEDZjW
I have transcribed it, clang-formatted it, added some comments, and made
the tests fit into a unittest file.
I have also switched llvm::unique_function over to use these new, much
more portable traits. =D
Hopefully this will fix the build bot breakage from my prior commit.
llvm-svn: 336161
a37bbe946c