rustc: implement pic args

docs/markdown/snippets/rustc-improvements.md

@@ -3,3 +3,4 @@
 - Werror now works, this set's `-D warnings`, which will cause rustc to error
   for every warning not explicitly disabled
 - warning levels have been implemented
+- support for meson's pic has been enabled

mesonbuild/compilers/rust.py

@@ -187,3 +187,12 @@ class RustCompiler(Compiler):
 
     def get_no_warn_args(self) -> T.List[str]:
         return self._WARNING_LEVELS["0"]
+
+    def get_pic_args(self) -> T.List[str]:
+        # This defaults to
+        return ['-C', 'relocation-model=pic']
+
+    def get_pie_args(self) -> T.List[str]:
+        # Rustc currently has no way to toggle this, it's controlled by whether
+        # pic is on by rustc
+        return []