Handle glibc partial header inclusions

Handle glibc partial header inclusions

The glibc headers use selective inclusions through the __need_NAME
mechanism to avoid circular dependencies.

The problem is that if we are being overlaid, and have been requested
a partial inclusion, when we pass control to the system header, then
we might miss definitions needed by our own header, resulting in build
failures.

Workaround that by catching current partial requests, and skip the
current inclusion.