Verify floating point inline asm register allocation works

[MabezDev]

This is a bug in the current LLVM backend, should be fixed in the future.

Test case:

Choosing a specific register:

let _x: f32;
unsafe {
    asm!(
        "lsi f0, a0, 152", out("f0") _x
    );
};

However class based register allocation doesn't seem to work yet:

let _x: f32;
unsafe {
    asm!(
        "lsi {}, a0, 152", out(freg) _x
    );
};

Fails with

error: invalid operand for instruction
  --> src/main.rs:76:14
   |
76 |             "lsi {}, a0, 152", out(freg) _x
   |              ^
   |
note: instantiated into assembly here
  --> <inline asm>:1:6
   |
1  |     lsi a8, a0, 152
   |         ^

error: could not compile `xtensa-quickstart` due to previous error

[KerryRJ]

Any reference for the bug?