libgo: add go-context.S in cmake file

Change-Id: I6d83e11b4bfe8bd06fc9ebe383a9898e933995f0
Reviewed-on: https://go-review.googlesource.com/c/gollvm/+/179638
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/libgo/CMakeLists.txt b/libgo/CMakeLists.txt
index f4d8c74..f2643a8 100644
--- a/libgo/CMakeLists.txt
+++ b/libgo/CMakeLists.txt
@@ -423,7 +423,8 @@
   "runtime/proc.c"
   "runtime/runtime_c.c"
   "runtime/stack.c"
-  "runtime/yield.c")
+  "runtime/yield.c"
+  "runtime/go-context.S")
 
 # C files that happen to be living in other packages.
 list(APPEND runtimecfiles