LLVM errors in MIR trans for struct and tuple ConstVals.

[solson]

These LLVM errors show up when compiling the following test cases with #[rustc_mir].

struct Point {
    _x: i32,
    _y: i32,
}

const STRUCT: Point = Point { _x: 42, _y: 42 };
let _struct = STRUCT;

// MIR: var0 = const expr Point{_x: 42, _y: 42,};

// Output:
// Stored value type does not match pointer operand type!
//   store { i32, i32 } { i32 42, i32 42 }, i64* %0, align 4
//  i64LLVM ERROR: Broken function found, compilation aborted!

const TUPLE: (i32, i32) = (42, 42);
let _tuple = TUPLE;

// MIR: var0 = const expr (42, 42);

// Output:
// Stored value type does not match pointer operand type!
//   store { i32, i32 } { i32 42, i32 42 }, i64* %0, align 4
//  i64LLVM ERROR: Broken function found, compilation aborted!

const TUPLE: (&'static str,) = ("ow",);
let _tuple = TUPLE;

// MIR: var0 = const expr ("ow",);

// Output:
// Invalid bitcast
// i8 addrspace(5)* bitcast ({ %str_slice } { %str_slice { i8* getelementptr inbounds ([2 x i8], [2 x i8]* @str2753, i32 0, i32 0), i64 2 } } to i8 addrspace(5)*)
// LLVM ERROR: Broken function found, compilation aborted!