w6c+selfhost: float globals — DATAW + LEAQ-indirect MOVSS/MOVSD

f32 → 4B slot, f64 → 8B. C cgen bakes the FLOATLIT bit pattern into
DATAW directly; selfhost emits zero-init only (its parser doesn't
lex N_FLOATLIT yet). Read/write goes LEAQ name(SB),CX + MOVSS/MOVSD
since w6a has no D_EXTERN operand form for SSE moves.

test/wcc/630_let_global.c

@@ -188,6 +188,50 @@ static const struct fixture fixtures[] = {
 		"};\n",
 		42,
 	},
+	{
+		"f64-literal-init",
+		/* `let pi: f64 = 3.14;` — DATAW bakes the 8 LE bytes of
+		 * the double directly. Read goes LEAQ name(SB),CX +
+		 * MOVSD (CX),X0; cast truncates to i32. */
+		"let pi: f64 = 7.5;\n"
+		"fn main() i32 = { return pi: i32; };\n",
+		7,
+	},
+	{
+		"f32-literal-init",
+		/* f32 globals are 4-byte slots; literal init bakes the
+		 * single-precision bit pattern. */
+		"let half: f32 = 4.25;\n"
+		"fn main() i32 = { return half: i32; };\n",
+		4,
+	},
+	{
+		"f64-zero-init",
+		"let z: f64;\n"
+		"fn main() i32 = { return z: i32; };\n",
+		0,
+	},
+	{
+		"f64-reassign",
+		/* Reassigning an f64 global goes LEAQ name(SB),CX +
+		 * MOVSD X0,(CX); read-back through the same shape. */
+		"let pi: f64 = 1.0;\n"
+		"fn main() i32 = {\n"
+		"\tpi = 7.5;\n"
+		"\treturn pi: i32;\n"
+		"};\n",
+		7,
+	},
+	{
+		"f64-arith",
+		"let a: f64 = 7.5;\n"
+		"let b: f64 = 4.25;\n"
+		"fn main() i32 = {\n"
+		"\tlet s: f64 = a + b;\n"
+		"\treturn s: i32;\n"
+		"};\n",
+		11,
+	},
 	{
 		"struct-narrow-field",
 		/* u8 field on a struct global. Read uses MOVZBQ, store