oeqa/sdk: extend rust test to also use a build script

The test for rust in the SDK is extended with the simplest
possible build script. This will make use of the host toolchain
for building build.rs before building the rust package for target.

(From OE-Core rev: 85a676da586f9b1085e62ef1325c9a58168390ae)

Signed-off-by: Peter Bergin <peter@berginkonsult.se>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/sdk/files/rust/hello/build.rs

@@ -0,0 +1,3 @@
+/* This is the simplest build script just to invoke host compiler
+   in the build process. */
+fn main() {}