Do not use named function labels if function names are not unique.

test/libsolidity/semanticTests/inlineAssembly/function_name_clash.sol

@@ -0,0 +1,13 @@
+contract C {
+  function f() public pure returns (uint r) {
+    assembly { function f() -> x { x := 1 } r := f() }
+  }
+  function g() public pure returns (uint r) {
+    assembly { function f() -> x { x := 2 } r := f() }
+  }
+}
+// ====
+// compileViaYul: also
+// ----
+// f() -> 1
+// g() -> 2