The <filename>assert.h</filename> header shall define the
<function>assert</function> macro. It refers to the macro
<constant>NDEBUG</constant>, which is not defined in this
header.
If <constant>NDEBUG</constant> is defined before the inclusion of
this header, the <function>assert</function> macro shall be defined
as described below, otherwise the macro shall behave as described
in <function>assert</function> in ISO/IEC 9945 POSIX.
