runtime: rename gothrow to throw

Rename "gothrow" to "throw" now that the C version of "throw"
is no longer needed.

This change is purely mechanical except in panic.go where the
old version of "throw" has been deleted.

sed -i "" 's/[[:<:]]gothrow[[:>:]]/throw/g' runtime/*.go

Change-Id: Icf0752299c35958b92870a97111c67bcd9159dc3
Reviewed-on: https://go-review.googlesource.com/2150
Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>
diff --git a/src/runtime/os1_plan9.go b/src/runtime/os1_plan9.go
index aa9d67f..63bba7c 100644
--- a/src/runtime/os1_plan9.go
+++ b/src/runtime/os1_plan9.go
@@ -194,7 +194,7 @@
 	}
 	pid := rfork(_RFPROC | _RFMEM | _RFNOWAIT)
 	if pid < 0 {
-		gothrow("newosproc: rfork failed")
+		throw("newosproc: rfork failed")
 	}
 	if pid == 0 {
 		tstart_plan9(mp)