https://codereview.chromium.org/1816333002 added "/fastfail" to the Windows linker flags. The LLD bots have been red since then (https://build.chromium.org/p/chromium.fyi/builders/CrWinClangLLD/builds/3547/steps/compile/logs/stdio) with

"Could not open /fastfail: no such file or directory"

It's probably fine to just silently parse and ignore that flag in lld-link.

("/fastfail should get us crash dumps when the linker crashes, which it
has been doing." says the CL description.)

It'd be good to fix this before the next clang roll, so that we have the fix in the next prebuilt package.