Reduce memory requirement to linux LTO builds to speed up bots.

The new requirements won't be enough for the official bots,
but the old requirements made all the bots to be extremely
slow (5-7 hours), and we don't run official bots as of now,
because that was too slow for CFI launch.

Reverting to the settings good enough for development, and keep in mind,
that we need to do something about the memory consumption for LTO builds
before we could attempt to launch again.

BUG=570227,464797

Review URL: https://codereview.chromium.org/1553093004

Cr-Original-Commit-Position: refs/heads/master@{#367323}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 61e70ccb5957620f3329f07ef79a76b81c96044b

toolchain/get_concurrent_links.py

@@ -53,9 +53,9 @@ def _GetDefaultConcurrentLinks(is_lto):
           # Allow 8Gb per link on Linux because Gold is quite memory hungry
           mem_per_link_gb = 8
           if is_lto:
-            mem_total_gb -= 20 # Reserve
+            mem_total_gb -= 10 # Reserve
             # For LTO builds the RAM requirements are even higher
-            mem_per_link_gb = 32
+            mem_per_link_gb = 16
           return int(max(1, mem_total_gb / mem_per_link_gb))
     return 1
   elif sys.platform == 'darwin':