Reserve more RAM per Gold process.

The current settings are too agressive even given the fact that
all the bots have 200+ GB RAM, and there's not so many large targets.
OOMs were observed:
https://build.chromium.org/p/chromium.fyi/builders/LTO%20Linux/builds/500

BUG=453195

Review-Url: https://codereview.chromium.org/1989083003
Cr-Original-Commit-Position: refs/heads/master@{#394423}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: b1e7d762e134b94196f551667ed31535b701e76e

toolchain/get_concurrent_links.py

@@ -55,7 +55,7 @@ def _GetDefaultConcurrentLinks(is_lto):
           if is_lto:
             mem_total_gb -= 10 # Reserve
             # For LTO builds the RAM requirements are even higher
-            mem_per_link_gb = 16
+            mem_per_link_gb = 24
           return int(max(1, mem_total_gb / mem_per_link_gb))
     return 1
   elif sys.platform == 'darwin':