Нельзя их использовать......
А вот и решение прямо из сорцов гцц
/* As the last action in this file, we poison the identifiers that
shouldn't be used. Note, luckily gcc-3.0's token-based integrated
preprocessor won't trip on poisoned identifiers that arrive from
the expansion of macros. E.g. #define strrchr rindex, won't error
if rindex is poisoned after this directive is issued and later on
strrchr is called.
Note: We define bypass macros for the few cases where we really
want to use the libc memory allocation routines. Otherwise we
insist you use the "x" versions from libiberty. */
#define really_call_malloc malloc
#define really_call_calloc calloc
#define really_call_realloc realloc