Inconsistent opaque type representation

Input C/C++ Header

template <class a> class Range { a b, c; };
typedef Range<const char *> StringPiece;
typedef Range<char> MutableStringPiece;
Range<char const *> d() {}

Bindgen Invocation

$ bindgen input.h --whitelist-type '(Mutable)?StringPiece'     --generate=types     --opaque-type '(Mutable)?StringPiece'     --no-layout-tests -- -x c++ -std=gnu++14

Actual Results

/* automatically generated by rust-bindgen */

pub type StringPiece = [u64; 2usize];
pub type MutableStringPiece = u8;

Expected Results

pub type StringPiece = [u64; 2usize];
pub type MutableStringPiece = [u64; 2usize];

StringPiece has a Rust type which correctly reflects its representation: [u64; 2size], which allows the Rust version of the type to be moved around etc. The MutableStringPiece is misrepresented by u8, which results in runtime errors because only the first byte is moved.

It looks like the d() function is what makes the difference; if I remove this then both StringPiece and MutableStringPiece get the same incorrect u8 representation.

This seems to be a regression introduced about 0.31, but I haven't checked specifically.

cc @kulshrax

Reproduce the issue with the shown input.h contents and bindgen invocation, then compare the generated StringPiece and MutableStringPiece aliases. Trace the opaque-type representation path, including the effect of d(), and verify that both aliases preserve the expected [u64; 2usize] representation without the first-byte-only behavior.