Rationalize visibility.

If it's C or POSIX, it's in. If it's BSD or GNU, it's guarded by __USE_BSD
or __USE_GNU.

Bug: https://code.google.com/p/android/issues/detail?id=194631
Change-Id: Ife51a21c2b37b060db56780d29c929805b199cb6
diff --git a/libc/include/complex.h b/libc/include/complex.h
index 66ea97e..e874e1c 100644
--- a/libc/include/complex.h
+++ b/libc/include/complex.h
@@ -43,7 +43,7 @@
 #define	complex		_Complex
 #define	I		_Complex_I
 
-#if __ISO_C_VISIBLE >= 2011
+#if __STDC_VERSION__ >= 201112L
 #ifdef __clang__
 #define	CMPLX(x, y)	((double complex){ x, y })
 #define	CMPLXF(x, y)	((float complex){ x, y })
@@ -53,7 +53,7 @@
 #define	CMPLXF(x, y)	__builtin_complex((float)(x), (float)(y))
 #define	CMPLXL(x, y)	__builtin_complex((long double)(x), (long double)(y))
 #endif
-#endif /* __ISO_C_VISIBLE >= 2011 */
+#endif
 
 __BEGIN_DECLS
 #pragma GCC visibility push(default)