Implement LWG-4294 bitset(const CharT*) constructor needs to be constrained

[frederick-vs-ja]

Fixes #5858.

Unblocked libcxx test(s):

• std/utilities/template.bitset/bitset.cons/string_ctor.pass.cpp

[StephanTLavavej]

Examining the test artifacts:

C:\Users\stl\Downloads>py D:\GitHub\STL\tools\scripts\print_failures.py test-results.xml
name: libc++.std/utilities/template_bitset/bitset_cons
No output, possibly because this was an XPASS.

[frederick-vs-ja]

Examining the test artifacts:

C:\Users\stl\Downloads>py D:\GitHub\STL\tools\scripts\print_failures.py test-results.xml
name: libc++.std/utilities/template_bitset/bitset_cons
No output, possibly because this was an XPASS.

Ah, thanks! The XPASS test is std/utilities/template.bitset/bitset.cons/string_ctor.pass.cpp.

This test expects that bitset isn't constructible from non-trivially-copyable Nonsense type in the immediate context, which is the result of LWG-4294.
https://github.com/llvm/llvm-project/blob/e02fdf0fcea3c02dc0eb692bc38042f9681e4afd/libcxx/test/std/utilities/template.bitset/bitset.cons/string_ctor.pass.cpp#L128-L134
And previously we treated that as non-Standard behavior.

STL/tests/libcxx/expected_results.txt

Lines 80 to 81 in ab6dec6

	# Testing nonstandard behavior
	std/utilities/template.bitset/bitset.cons/string_ctor.pass.cpp FAIL