Remove unnecessary exec_script for secondary toolchain

Change-Id: I457dd7e9cc616038b50122e1fc12266ca24df92f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2075037
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744807}

build/toolchain/BUILD.gn

@@ -10,11 +10,11 @@ declare_args() {
   action_pool_depth = -1
 }
 
-if (action_pool_depth == -1 || use_goma) {
-  action_pool_depth = exec_script("get_cpu_count.py", [], "value")
-}
-
 if (current_toolchain == default_toolchain) {
+  if (action_pool_depth == -1 || use_goma) {
+    action_pool_depth = exec_script("get_cpu_count.py", [], "value")
+  }
+
   pool("link_pool") {
     depth = concurrent_links
   }