Serialization support for TagDecl::IsCompleteDefinitionRequired

Requested by Richard Smith in post-commit review of r186262

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186266 91177308-0d34-0410-b5e6-96231b3b80d8
If an unimported submodule of an imported module contains a declaration of a
global allocation or deallocation function, that should not cause that global
allocation or deallocation function to become unavailable.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186270 91177308-0d34-0410-b5e6-96231b3b80d8
Add missing include guards into headers in lib/Headers. While it may appear
that these headers should not be included more than once, they are in fact
included twice when building our builtins module (in order for it to generate
submodules for them), and without this, any modular build enabling AVX and
including any builtin header fails.

Testing this is tricky because including any of these headers in a modular
build is liable to fail, due to unrelated builtin headers in the same module
including headers which might not be available on the system running the tests.
Suggestion on that front are welcome (but we're getting close to being able to
run a buildbot that has modules enabled for all tests, which would nicely solve
the testing problem).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186275 91177308-0d34-0410-b5e6-96231b3b80d8