compilers: add Rustup libdir even if there is no other rpath argument

RustCompiler.build_rpath_args works by appending the directory to the
arguments computed by self.linker.build_rpath_args.  This does not
work if there is no argument to begin with, which happens for example
in program crates.

Use the new extra_paths argument to force inclusion of the libdir into
the rpath of the binary, even in that case.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

mesonbuild/compilers/rust.py

@@ -202,15 +202,15 @@ def get_optimization_args(self, optimization_level: str) -> T.List[str]:
     def build_rpath_args(self, env: 'Environment', build_dir: str, from_dir: str,
                          rpath_paths: T.Tuple[str, ...], build_rpath: str,
                          install_rpath: str) -> T.Tuple[T.List[str], T.Set[bytes]]:
-        args, to_remove = super().build_rpath_args(env, build_dir, from_dir, rpath_paths,
-                                                   build_rpath, install_rpath)
+        # add rustc's sysroot to account for rustup installations
+        args, to_remove = self.linker.build_rpath_args(env, build_dir, from_dir, rpath_paths,
+                                                       build_rpath, install_rpath,
+                                                       [self.get_target_libdir()])
 
-        # ... but then add rustc's sysroot to account for rustup
-        # installations
         rustc_rpath_args = []
         for arg in args:
             rustc_rpath_args.append('-C')
-            rustc_rpath_args.append(f'link-arg={arg}:{self.get_target_libdir()}')
+            rustc_rpath_args.append('link-arg=' + arg)
         return rustc_rpath_args, to_remove
 
     def compute_parameters_with_absolute_paths(self, parameter_list: T.List[str],