Reorganize inclusion per P0063R3 to reduce deprecation warnings

Author: frederick-vs-ja

libcxx/include/complex.h

@@ -24,7 +24,11 @@
 #endif
 
 #ifdef __cplusplus
-#  include <ccomplex>
+#  if _LIBCPP_STD_VER >= 17
+#    include <complex>
+#  else
+#    include <ccomplex>
+#  endif
 #elif __has_include_next(<complex.h>)
 #  include_next <complex.h>
 #endif

libcxx/include/ctgmath

@@ -18,7 +18,12 @@
 
 */
 
-#include <ccomplex>
+#if _LIBCPP_STD_VER >= 17
+#  include <complex>
+#else
+#  include <ccomplex>
+#endif
+
 #include <cmath>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)

libcxx/include/tgmath.h

@@ -24,7 +24,12 @@
 #endif
 
 #ifdef __cplusplus
-#  include <ctgmath>
+#  if _LIBCPP_STD_VER >= 17
+#    include <complex>
+#    include <cmath>
+#  else
+#    include <ctgmath>
+#  endif
 #else
 #  if __has_include_next(<tgmath.h>)
 #    include_next <tgmath.h>

libcxx/test/std/depr/depr.cpp.headers/ctgmath.verify.cpp

@@ -15,12 +15,10 @@
 #include "test_macros.h"
 
 #if TEST_STD_VER >= 20
-// expected-warning {{'__standard_header_ccomplex' is deprecated: removed in C++20}}
 // expected-warning {{'__standard_header_ctgmath' is deprecated: removed in C++20}}
 
 #  include <ctgmath>
 #else
-// expected-warning {{'__standard_header_ccomplex' is deprecated}}
 // expected-warning {{'__standard_header_ctgmath' is deprecated}}
 
 #  include <ctgmath>