This patch fixes the location of the llvm remote inspection headers for
MSVC header lookup. MSVC appears to search in the directory of the
current header before returning to the specified header search
directories. When building SwiftRemoteMirror, the file contains a
reference to `swift/RemoteInspection/ReflectionContext.h`. Under
RelfectionContext.h, there is an include of "llvm/BinaryFormat/COFF.h".
Because there is an `llvm` and `llvm-c` directory inside of
`swift/RemoteInspection/`, and `ReflectionContext.h` is in that
directory, MSVC is expanding the `COFF.h` inside of the
RemoteInspection headers instead of the copy in LLVM itself, resulting
in eventually finding usages of `countPopulation` instead of using the
new `llvm::popcount` API, ultimately resulting in a build failure.
The fix is to ensure that the `llvm` header directory does not live
immediately next to the headers in RemoteInspection, but instead offset
them by one. The LLVM headers copied into RemoteInspection are supposed
to be used when compiling the runtime libraries, so I chose the name
"RuntimeHeaders".
