tree-cfg: Reject constants and addr on lhs for assign single [PR120921]

tree-cfg: Reject constants and addr on lhs for assign single [PR120921]

For GIMPLE_SINGLE_RHS, we don't currently test LHS for some invalid cases.
In this case all constants and ADDR_EXPR should be invalid on the LHS.
Also for vector (non-empty) constructors, the LHS needs to be an is_gimple_reg.

This adds the checks.
Also this fixes the following gimple testcase so it no longer ICEs, all functions are correctly rejected:
```
typedef vector int vi;

void __GIMPLE b1(int t) {
  1 = t;
}
void __GIMPLE b2() {
  1 = 2;
}
void __GIMPLE b3(int t, int t1) {
  &t1 = &t;
}
void __GIMPLE b4(vi t, vi t1) {
  _Literal(vi){0} = _Literal(vi){1};
}
void __GIMPLE b5(vi t, vi t1) {
  _Literal(vi){t} = _Literal(vi){t1};
}
```

Bootstrapped and tested on x86_64-linux-gnu.

	PR middle-end/120921
gcc/ChangeLog:

	* tree-cfg.cc (verify_gimple_assign_single): Reject constant and address expression LHS.
	For non-empty vector constructors, make sure the LHS is an is_gimple_reg.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>