Add modules support for lldb headers in include/
This patch adds a modulemap which allows compiling the lldb headers into C++ modules
(for example in builds with LLVM_ENABLE_MODULES=On).
Even though most of the affected code has been cleaned up to work with the more strict
C++ module semantics, there are still some workarounds left in the current modulemap
(the most obvious one is the big lldb wrapper module).
It also moves the Obj-C++ files in lldb to their own subdirectories. This was necessary
because we need to filter out the modules flags for this code.
Note: With the latest clang and libstdc++ it seems necessary to have a STL C++ module
to get a working LLVM_ENABLE_MODULES build for lldb. Otherwise clang will falsely
detect ODR violations in the textually included STL code inside the lldb modules.
Reviewers: aprantl, bruno
Reviewed By: aprantl, bruno
Subscribers: mgorny, yamaguchi, v.g.vassilev, lldb-commits
Differential Revision: https://reviews.llvm.org/D47929