Give more RAM per ld process.
Give more RAM per ld process.

It has been observed that occasionally official buildbots
would crash with OOM, when building Chrome with CFI
(and thus with LTO). This CL reduces the number of
concurrent link processes to avoid this problem.

BUG=464797

Review URL: https://codereview.chromium.org/1509733004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#364173}

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