Declare dependency on android_filesystem_config.h

android_filesystem_config.h comes from a directory outside bionic/libc
so it can't be referenced directly, add it as a source file through
a filegroup module.

Bug: 34283327
Test: builds
Test: libc rebuilds after touch system/core/include/private/android_filesystem_config.h
Change-Id: I90f6b7b25b70842b8619d558074449f13e6e6b03