As an extension the C++ version of <complex.h> includes the C version,
but that defines macros with non-reserved names that should not be
defined in ISO C++. Only include the C header for non-strict modes, or
for pre-C++11 (because C++98 doesn't mention <complex.h> at all).

	PR libstdc++/59087
	PR libstdc++/82417
	* include/c_compatibility/complex.h [!C++98 && __STRICT_ANSI__]: Do
	not include C library's <complex.h>.
	* testsuite/26_numerics/complex/c99.cc: Depend on __STRICT_ANSI__.
	* testsuite/26_numerics/headers/complex.h/std_c++11.h: New test.
	* testsuite/26_numerics/headers/complex.h/std_gnu++11.h: New test.
	* testsuite/26_numerics/headers/complex.h/std_c++98.h: New test.

From-SVN: r253581