Wrap sprintf()/snprintf() macros to prevent expansion errors.

Previously, FORTIFY_SOURCE used single macros to define these standard
functions for use with clang. This can cause conflicts with other macros used
to call these functions, particularly when those macros expand the number of
arguments to the function. This change wraps our macro definitions, so that
expansion properly takes place for programmer arguments first.

Change-Id: I55929b1fd2a643b9d14a17631c4bcab3b0b712cf