oeqa/selftest/rust: strip debug symbols from test binaries

oeqa/selftest/rust: strip debug symbols from test binaries

Strip debug symbols from test binaries using RUSTFLAGS='-C strip=debuginfo'
to reduce binary sizes from 300+ MB to ~140 MB.

This is especially critical for PowerPC mac99 which has a hardcoded 768MB
RAM limit in QEMU. Without stripping, test binaries uploaded to /tmp (tmpfs)
cause 'No space left on device' errors during test execution.

The size reduction also benefits all other architectures by reducing
memory pressure and upload times during testing.

Signed-off-by: Peter Tatrai <peter.tatrai.ext@siemens.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>