ld: fix alignment of rodata section on Plan 9

This was causing a panic in the reflect package
since type.* pointers with their low bits set are
assumed to have certain flags set that disallow
the use of reflection.

Thanks to Pavel and Taru for help tracking down
this bug.

R=rsc, paulzhol, taruti
CC=golang-dev
https://golang.org/cl/4511041

src/cmd/8l/obj.c

@@ -188,7 +188,7 @@ main(int argc, char *argv[])
 		if(INITDAT == -1)
 			INITDAT = 0;
 		if(INITRND == -1)
-			INITRND = 1;
+			INITRND = 4096;
 		break;
 	case Hmsdoscom:	/* MS-DOS .COM */
 		HEADR = 0;

src/cmd/ld/data.c

@@ -899,10 +899,8 @@ address(void)
 	segdata.fileoff = va - segtext.vaddr + segtext.fileoff;
 	if(HEADTYPE == Hwindows)
 		segdata.fileoff = segtext.fileoff + rnd(segtext.len, PEFILEALIGN);
-	if(HEADTYPE == Hplan9x32) {
-		segdata.vaddr = va = rnd(va, 4096);
+	if(HEADTYPE == Hplan9x32)
 		segdata.fileoff = segtext.fileoff + segtext.filelen;
-	}
 	for(s=segdata.sect; s != nil; s=s->next) {
 		s->vaddr = va;
 		va += s->len;