rust: Add missing variation -D flags to bindgen.

rust_bindgen calls are missing a large set of -D cflags which control
how headers are interpretted for certain variations (such as
-D__ANDROID_VNDK__). This CL introduces the full set of these flags.

Bug: 205609024
Test: rust_bindgen vendor variant builds correctly.

Change-Id: Id781c1f88352e9c238c49619f0dce20f804cfc77