tests: Fix duplicated-path-in-error fail with musl

musl's dlopen returns a different error than glibc, which contains the
name of the file. This would cause the test to fail, since the filename
would appear twice in the output (once in the error from rustc, once in
the error message from musl). Substitute the error message with the one
from glibc to work around this.

Signed-off-by: Jens Reidel <[email protected]>

Author: Gelbpunkt

tests/ui/codegen/duplicated-path-in-error.rs

@@ -1,5 +1,6 @@
 //@ only-linux
 //@ compile-flags: -Zcodegen-backend=/non-existing-one.so
+//@ normalize-stderr: "Error loading shared library .+:" -> "cannot open shared object file:"
 
 // This test ensures that the error of the "not found dylib" doesn't duplicate
 // the path of the dylib.