gollvm: add missing libgo dependent C file

Update the cmake rules for libgo to add a missing dependent
C source file (dir_gccgo_c.c in the "os" package).

Updates golang/go#43583.

Change-Id: I27820052aa3d22099a63213afa1a27ea94f92cff
Reviewed-on: https://go-review.googlesource.com/c/gollvm/+/282613
Trust: Than McIntosh <thanm@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/libgo/CMakeLists.txt b/libgo/CMakeLists.txt
index 7da82c8..149ea02 100644
--- a/libgo/CMakeLists.txt
+++ b/libgo/CMakeLists.txt
@@ -464,6 +464,7 @@
 list(APPEND runtimecfiles
   "go/internal/bytealg/bytealg.c"
   "go/log/syslog/syslog_c.c"
+  "go/os/dir_gccgo_c.c"
   "go/reflect/makefunc_ffi_c.c"
   "go/runtime/internal/atomic/atomic.c"
   "go/internal/cpu/cpu_gccgo.c"