Fix for PR43175: compiler crash when trying to emit noncapturable

constant.

If the constexpr variable is partially initialized, the initializer can
be emitted as the structure, not as an array, because of some early
optimizations. The llvm variable gets the type from this constant and,
thus, gets the type which is pointer to struct rather than pointer to an
array. We need to convert this type to be truely array, otherwise it may
lead to the compiler crash when trying to emit array subscript
expression.

llvm-svn: 371548