gollvm: update cmakelists to import correct c file

CMakeLists.txt currently tries to include /x/sys/cpu/cpu_gccgo.c
which is no longer there, thus causing build to fail for x86 platform
architecture. This updates CMakeLists.txt to import correct C file
from the golang/sys package which is cpu_gccgo_x86.c from x86.

Fixes golang/go#40258

Change-Id: I80be54daee277a53906031b3f69772defd5f853f
Reviewed-on: https://go-review.googlesource.com/c/gollvm/+/246318
Reviewed-by: Cherry Zhang <cherryyz@google.com>
diff --git a/libgo/CMakeLists.txt b/libgo/CMakeLists.txt
index 7ba6e3d..08b9f2c 100644
--- a/libgo/CMakeLists.txt
+++ b/libgo/CMakeLists.txt
@@ -446,7 +446,7 @@
 if (NOT ${goarch} STREQUAL "arm64")
   list(APPEND runtimecfiles
-    "go/golang.org/x/sys/cpu/cpu_gccgo.c")
+    "go/golang.org/x/sys/cpu/cpu_gccgo_x86.c")
 # Linux-specific C files.