nir: Add support for 1-bit data types

This commit adds support for 1-bit Booleans and integers.  Booleans
obviously take a value of true or false.  Because we have to define the
semantics of 1-bit signed and unsigned integers, we define uint1_t to
take values of 0 and 1 and int1_t to take values of 0 and -1.  1-bit
arithmetic is then well-defined in the usual way, just with fewer bits.
The definition of int1_t and uint1_t doesn't usually matter but we do
need something for purposes of constant folding.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Tested-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

src/compiler/nir/nir_opt_constant_folding.c

@@ -88,6 +88,9 @@ constant_fold_alu_instr(nir_alu_instr *instr, void *mem_ctx)
          case 8:
             src[i].u8[j] = load_const->value.u8[instr->src[i].swizzle[j]];
             break;
+         case 1:
+            src[i].b[j] = load_const->value.b[instr->src[i].swizzle[j]];
+            break;
          default:
             unreachable("Invalid bit size");
          }