Test building of libraries with rustc logging enabled

Author: tmiasko

src/test/ui/auxiliary/rustc-rust-log-aux.rs

@@ -0,0 +1 @@
+// rustc-env:RUSTC_LOG=debug

src/test/ui/rustc-rust-log.rs

@@ -8,7 +8,7 @@
 // dont-check-compiler-stdout
 // dont-check-compiler-stderr
 // compile-flags: --error-format human
-
+// aux-build: rustc-rust-log-aux.rs
 // rustc-env:RUSTC_LOG=debug
 
 fn main() {}