libstdc++: Rename __cpp_lib_constexpr_invoke macro

This macro was renamed after it was added to the working draft, but we
never renamed it  in libstdc++. We haven't made a release with the old
macro name, so I see no need to keep it around.

	* include/std/functional (__cpp_lib_constexpr_invoke): Rename to
	__cpp_lib_constexpr_functional.
	* include/std/version (__cpp_lib_constexpr_invoke): Likewise.
	* testsuite/20_util/function_objects/invoke/constexpr.cc: Adjust.

libstdc++-v3/ChangeLog

 2020-04-22  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/functional (__cpp_lib_constexpr_invoke): Rename to
+	__cpp_lib_constexpr_functional.
+	* include/std/version (__cpp_lib_constexpr_invoke): Likewise.
+	* testsuite/20_util/function_objects/invoke/constexpr.cc: Adjust.
+
 	* include/bits/ptr_traits.h (__cpp_lib_constexpr_memory): Define to
 	indicate P1006R1 support.
 	(__cpp_lib_to_address): Define to indicate P0653R2 support.

libstdc++-v3/include/std/functional

@@ -76,7 +76,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if __cplusplus >= 201703L
 # define __cpp_lib_invoke 201411L
 # if __cplusplus > 201703L
-#  define __cpp_lib_constexpr_invoke 201907L
+#  define __cpp_lib_constexpr_functional 201907L
 # endif
 
   /// Invoke a callable object.

libstdc++-v3/include/std/version

@@ -190,7 +190,7 @@
 #define __cpp_lib_constexpr_algorithms 201806L
 #define __cpp_lib_constexpr_complex 201711L
 #define __cpp_lib_constexpr_dynamic_alloc 201907L
-#define __cpp_lib_constexpr_invoke 201907L
+#define __cpp_lib_constexpr_functional 201907L
 #define __cpp_lib_constexpr_memory 201811L
 #define __cpp_lib_constexpr_numeric 201911L
 #define __cpp_lib_erase_if 202002L

libstdc++-v3/testsuite/20_util/function_objects/invoke/constexpr.cc

@@ -20,9 +20,9 @@
 
 #include <functional>
 
-#ifndef __cpp_lib_constexpr_invoke
+#ifndef __cpp_lib_constexpr_functional
 # error "Feature test macro for constexpr invoke is missing"
-#elif __cpp_lib_constexpr_invoke < 201907L
+#elif __cpp_lib_constexpr_functional < 201907L
 # error "Feature test macro for constexpr invoke has wrong value"
 #endif