rust-cross: Fix directory not deleted for race glibc vs. musl

Use different recipe names for the two different targets so that
when switching libcs overlapping files in the sysroot don't cause
issues.

Signed-off-by: Pgowda <pgowda.cve@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>