test: re-enable test on riscv64 now that it supports external linking

Update #36739

Change-Id: I14ab2cd0e29966b9a2f992e8c3bcb415203e63e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/321449
Trust: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

test/fixedbugs/issue10607.go

@@ -1,4 +1,4 @@
-// +build linux,!ppc64,!riscv64,gc
+// +build linux,!ppc64,gc
 // run
 
 // Copyright 2015 The Go Authors. All rights reserved.
@@ -8,9 +8,6 @@
 // Test that a -B option is passed through when using both internal
 // and external linking mode.
 
-// TODO(jsing): Re-enable on riscv64 when it has support for external
-// linking - see golang.org/issue/36739
-
 package main
 
 import (