[C++ PAtch] More C++11 and C++14 constexpr work

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

the below tries to make progress on some relatively easy issues I 
noticed while working on c++/55250. At least:
1- We rejected using declarations and using directives in constructors.
2- In C++14 mode we rejected compound-statements both in constructors 
and elsewhere (and in C++11 we provided both the pedwarn and then an 
hard error)
3- In C++14 mode we rejected local variables in constructors.

The patch itself uses quite straightforward strategies: 
check_constexpr_ctor_body is extended via the new 
check_constexpr_ctor_body_1; recursion on BIND_EXPRs takes care of 
compound-statements; the parser is tweaked to suppress the 
"compound-statement in constexpr function" pedwarn in C++14 mode.

Tested x86_64-linux.

Thanks,
Paolo.

//////////////////////

Attachment: CL_constexpr
Description: Text document

Attachment: patch_constexpr
Description: Text document