[docs] Prevent O0 optnone for opt input

If we just compile with -O0, clang will add optnone attributes
everywhere, so opt won't actually be able to perform any passes.
Instruct clang to not emit the optnone so opt can do its thing.

Differential Revision: https://reviews.llvm.org/D56950

llvm-svn: 352550

Author: smeenai

llvm/docs/HowToSubmitABug.rst

@@ -84,8 +84,8 @@ Compile-time optimization bugs
 ------------------------------
 
 If you find that a bug crashes in the optimizer, compile your test-case to a
-``.bc`` file by passing "``-emit-llvm -O0 -c -o foo.bc``".
-Then run:
+``.bc`` file by passing "``-emit-llvm -O1 -Xclang -disable-llvm-passes -c -o
+foo.bc``".  Then run:
 
 .. code-block:: bash