AC_FUNC_{M,RE}ALLOC are not cross-compiling aware

Found this bug on Autoconf 2.69 The AC_FUNC_MALLOC and AC_FUNC_REALLOC macros check for runtime behaviors of `malloc` and `realloc` respectively. However, both checks silently evaluate to "no" when cross-compiling. This is a bug, because: 1. They do not emit a warning on cross-compiling mode.

AC_FUNC_{M,RE}ALLOC are not cross-compiling aware

Found this bug on Autoconf 2.69 The AC_FUNC_MALLOC and AC_FUNC_REALLOC macros check for runtime behaviors of `malloc` and `realloc` respectively. However, both checks silently evaluate to "no" when cross-compiling. This is a bug, because: 1. They do not emit a warning on cross-compiling mode.