Use descriptive message if list initializer is incorrectly parenthesized.

Use descriptive message if list initializer is incorrectly parenthesized.

If initializer contains parentheses around braced list where it is not allowed,
as in construct int({0}), clang issued message like `functional-style cast
from 'void' to 'int' is not allowed`, which does not help much. Both gcc and
msvc issue message `list-initializer for non-class type must not be
parenthesized`, which is more descriptive. This change implements similar
message for clang.

Differential Revision: https://reviews.llvm.org/D25816

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@286721 91177308-0d34-0410-b5e6-96231b3b80d8