Add a placeholder target for librustc_demangle_static. am: 552e7417a7 am: ec2f2d4656

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/rustc-demangle-capi/+/2400819

Change-Id: Ic5da1634dd3b043b1611333e2a9a61000f2018b9
Signed-off-by: Automerger Merge Worker <[email protected]>