Bump default MAXTSIZ (kern.maxtsiz) from 128MB to 32GB. The old limit

prevents one from running eg clang built with debug; the new one is
arbitrary (equal to MAXDSIZ) and... well, should be quite future-proof.

Same fix might be applicable to other 64 bit architectures; I'll ask
their respective maintainers to make sure it won't break anything.

Reviewed by:	kib
MFC after:	2 weeks
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D10758

sys/amd64/include/vmparam.h

@@ -52,7 +52,7 @@
 /*
  * Virtual memory related constants, all in bytes
  */
-#define	MAXTSIZ		(128UL*1024*1024)	/* max text size */
+#define	MAXTSIZ		(32768UL*1024*1024)	/* max text size */
 #ifndef DFLDSIZ
 #define	DFLDSIZ		(32768UL*1024*1024)	/* initial data size limit */
 #endif