fix(format): preserve macro adjacency and continuation bodies

The canonical spelling of a #define line glued a '(' to the macro name
whatever the input's spacing, turning an object macro whose body opens
with a parenthesis into a parameterised one, and it flattened the
backslash continuations of a multi-line body into one physical line,
fusing the statements the expansion splits at those boundaries.  Both
change what a valid file assembles to, so renderPreproc now keeps the
name's adjacency (the same column check the preprocessor applies) and
restores the continuation boundaries from the token positions.

Assisted-by: GLM 5.3

format/format_test.go

@@ -329,10 +329,12 @@ func TestSemicolonSeparators(t *testing.T) {
 		},
 		{
 			// The continuation-spliced macro shape of the runtime sources:
-			// the lexer makes one logical line of the backslash continuations.
+			// the lexer makes one logical line of the backslash continuations,
+			// and the canonical form restores them, because the expansion
+			// splits a macro body at those line boundaries.
 			name: "inside a macro body, continued",
 			in:   "#define MOVLTOREG(v, off) \\\n\tMOVL $v, AX; \\\n\tMOVL AX, ret+off(FP)\n",
-			want: "#define MOVLTOREG(v, off) MOVL $v, AX; MOVL AX, ret+off(FP)\n",
+			want: "#define MOVLTOREG(v, off) \\\n\tMOVL $v, AX; \\\n\tMOVL AX, ret+off(FP)\n",
 		},
 		{
 			name: "inside a macro body, one line",