Reword push_cc_arg() doc comments.

* Clarify that the flag is added after other arguments (although obvious from
  the function name),
* Push extraneous info to the second paragraph to display nicer in IDE
  completions,
* Reword the bits about nvcc and the `-Xcompiler` flag.

Author: mqudsi

src/lib.rs

@@ -3277,11 +3277,12 @@ impl Tool {
         self.removed_args.push(flag);
     }
 
-    /// Add a flag, and optionally prepend the NVCC wrapper flag "-Xcompiler".
+    /// Push a flag to the end of the compiler's arguments list.
     ///
-    /// Currently this is only used for compiling CUDA sources, since NVCC only
-    /// accepts a limited set of GNU-like flags, and the rest must be prefixed
-    /// with a "-Xcompiler" flag to get passed to the underlying C++ compiler.
+    /// Currently `-Xcompiler` is inserted before the passed flag when compiling
+    /// CUDA sources since NVCC only accepts a limited set of GNU-like flags,
+    /// while the rest must be prefixed with the `-Xcompiler` flag to get passed
+    /// to the underlying C++ compiler.
     fn push_cc_arg(&mut self, flag: OsString) {
         if self.cuda {
             self.args.push("-Xcompiler".into());