Crank MAXTSIZ to next pow2 (256MB) because a few piggy binaries

compiled with retpoline enabled are even piggier now.
diagnosed with robert kettenis and drahn

sys/arch/amd64/include/vmparam.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: vmparam.h,v 1.21 2015/02/08 03:48:25 deraadt Exp $	*/
+/*	$OpenBSD: vmparam.h,v 1.22 2019/01/03 18:59:27 deraadt Exp $	*/
 /*	$NetBSD: vmparam.h,v 1.1 2003/04/26 18:39:49 fvdl Exp $	*/
 
 /*-
@@ -55,7 +55,7 @@
 /*
  * Virtual memory related constants, all in bytes
  */
-#define	MAXTSIZ		((paddr_t)128*1024*1024)	/* max text size */
+#define	MAXTSIZ		((paddr_t)256*1024*1024)	/* max text size */
 #ifndef DFLDSIZ
 #define	DFLDSIZ		((paddr_t)128*1024*1024)	/* initial data size limit */
 #endif