1. Load the attached bigbug.el

2. open it in emacs and edit the definition of
   clang-project-default-settings, for example, remove "-v"

3. C-M-x the defcustom

4. C-h v clang-project-default-settings to show:

,----
| clang-project-default-settings is a variable defined in `bigbug.el'.
| Its value is (("SDKROOT" . "iphoneos")
|  ("OTHER_CFLAGS" "-ferror-limit=0" "-ObjC" "-DDEBUG=1" "-v"))
| 
| Original value was 
| (("SDKROOT" . "iphoneos")
|  ("OTHER_CFLAGS" "-ferror-limit=0" "-ObjC" "-DDEBUG=1"))
| 
| 
| Documentation:
| FIXME
| 
| You can customize this variable.
`----

i.e. C-M-x doesn't change the value of clang-project-default-settings,
this is opposite to the behaviour when lexical-binding is nil or in
previous emacsen.

Leo