The special operator
__has_cpp_attribute (operand) may be used
in ‘#if’ and ‘#elif’ expressions in C++ code to test whether
the attribute referenced by its operand is recognized by GCC.
__has_cpp_attribute (operand) is equivalent to
__has_attribute (operand) except that when operand
designates a supported standard attribute it evaluates to an integer
constant of the form
YYYYMM indicating the year and month when
the attribute was first introduced into the C++ standard. For additional
information including the dates of the introduction of current standard
attributes, see SD-6: SG10 Feature Test Recommendations.