[Bug c++/71543] [concepts] ICE on ill-formed declaration of a parameter with a constrained-type-specifier in a requires expression

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71543

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC 10 and above reject the code:
<source>:4:28: error: placeholder type not allowed in this context
    4 | concept bool C2 = requires(C1 c1) {};
      |                            ^~
<source>:4:36: error: expected primary-expression before '}' token
    4 | concept bool C2 = requires(C1 c1) {};
      |                                    ^
<source>:4:36: error: expected ';' before '}' token
    4 | concept bool C2 = requires(C1 c1) {};
      |                                    ^
      |                                    ;