Remove an outdated statement about debugging optimized code.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@197820 91177308-0d34-0410-b5e6-96231b3b80d8

docs/tools/clang.pod

@@ -310,8 +310,7 @@ Currently equivalent to B<-O3>
 =item B<-g>
 
 Generate debug information.  Note that Clang debug information works best at
-B<-O0>.  At higher optimization levels, only line number information is
-currently available.
+B<-O0>.
 
 =item B<-flimit-debug-info> B<-fno-limit-debug-info>