Reduce concurrently of LTO build.

The official build started to fail due to OOM from time to time.
Once we moved from full LTO to ThinLTO, this issue will go away completely.

BUG=650867

Review-Url: https://codereview.chromium.org/2378163002
Cr-Commit-Position: refs/heads/master@{#421607}

build/toolchain/concurrent_links.gni

@@ -22,8 +22,8 @@ declare_args() {
 if (concurrent_links == -1) {
   if (allow_posix_link_time_opt || is_cfi) {
     _args = [
-      "--mem_per_link_gb=24",
-      "--reserve_mem_gb=10",
+      "--mem_per_link_gb=26",
+      "--reserve_mem_gb=20",
     ]
   } else if (is_win) {
     _args = [ "--mem_per_link_gb=5" ]