Test: Clarify "non-standard extension"

[frederick-vs-ja]

We're currently saying "non-standard extension" in several test files.

STL/tests/std/tests/GH_000431_copy_move_family/test.cpp

Line 436 in 3f76681

if constexpr (is_convertible_v<void (*)(int), void*>) { // Test void (*)(int) => void* (non-standard extension)

STL/tests/std/tests/GH_000431_equal_family/test.cpp

Line 586 in 3f76681

if constexpr (is_convertible_v<void (*)(int), void*>) { // Test void (*)(int) == void* (non-standard extension)

STL/tests/std/tests/GH_000431_equal_memcmp_is_safe/test.compile.pass.cpp

Line 506 in 3f76681

// Converting from function pointers to void pointers is a non-standard extension

STL/tests/std/tests/GH_000431_iter_copy_move_cat/test.compile.pass.cpp

Line 419 in 3f76681

// Converting from function pointers to void pointers is a non-standard extension

STL/tests/std/tests/VSO_0000000_string_view_idl/test.cpp

Line 249 in 3f76681

// basic_string_view::_Copy_s() is a non-Standard extension that's unconditionally checked.

This is seemingly redundant, because every extension can hardly to be considered "standard extension". Perhaps it would be clearer to say "non-conforming/conformant" extension.

• For conversion from function pointers to void*, I believe this extension is non-conforming. As [conv.ptr]/2 only allows implicit conversion from pointer to object types to cv void*.
• For basic_string_view::_Copy_s(), I believe this extension is conforming because it's under an _Ugly name, and we can just say "an extension".

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There're also comments in <yvals_core.h> saying "non-Standard extension(s)". But as they refer to removed deprecation messages, I think we shouldn't modify them.

STL/stl/inc/yvals_core.h

Lines 1463 to 1468 in 3f76681

	// STL4043 was "stdext::checked_array_iterator, stdext::unchecked_array_iterator,
	// and related factory functions are non-Standard extensions and will be removed"
	// STL4044 was "The contents of the stdext::cvt namespace are non-Standard extensions and will be removed"
	// STL4045 was "The ipfx(), isfx(), opfx(), and osfx() functions are [...] non-Standard extensions"

STL/stl/inc/yvals_core.h

Line 1484 in 3f76681

// STL4048 was "locale::empty() is a non-Standard extension and will be removed in the future."

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It seems to be a good first issue Good for newcomers to improve the comments in these test files.

[StephanTLavavej]

In my opinion these comments are clear as-is and don't need to be changed. I'm willing to hear other opinions though.

[AlexGuteniev]

We have a precedent of saying just extension in <fstream> at least, maybe somewhere else.

I don't mean pleonasm here though.