[LLDB] Pass /std:... before -- on MSVC (llvm#141782)

From llvm#140761. `MsvcBuilder`
passed `/std:<value>` (if specified) after `--`, so the compiler would
interpret this as a file. This moves the argument before the `--`.

Author: Nerixyz

lldb/test/Shell/helper/build.py

@@ -683,14 +683,14 @@ def _get_compilation_command(self, source, obj):
             args.append("-fms-compatibility-version=19")
         args.append("/c")
 
+        if self.std:
+            args.append("/std:" + self.std)
+
         args.append("/Fo" + obj)
         if self.toolchain_type == "clang-cl":
             args.append("--")
         args.append(source)
 
-        if self.std:
-            args.append("/std:" + self.std)
-
         return ("compiling", [source], obj, self.compile_env, args)
 
     def _get_link_command(self):