[Bug bootstrap/63750] use of undeclared identifier 'do_not_use_isalnum_with_safe_ctype'

[howarth at bromo dot med.uc.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63750

--- Comment #4 from howarth at bromo dot med.uc.edu ---
Patch posted at https://gcc.gnu.org/ml/gcc-patches/2014-11/msg00661.html.

Note that the alternate approach of modifying gcc/system.h to include <string>
conditionally on __cplusplus before "safe-ctype.h" causes bootstrap breakage
elsewhere on darwin.