cmd/ld: increase number of ELF sections

On NetBSD a cgo enabled binary has more than 32 sections - bump NSECTS
so that we can actually link them successfully.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6261052

src/cmd/ld/elf.c

@@ -11,7 +11,7 @@
  * in order to write the code just once.  The 64-bit data structure is
  * written in the 32-bit format on the 32-bit machines.
  */
-#define	NSECT	32
+#define	NSECT	48
 
 int	iself;