This enables the LLD_IN_TEST=2 testing mode for
```
path/to/llvm-lit -sv --param RUN_LLD_MAIN_TWICE=1 lld/test/ELF
```
When `Fatal` is called, `RunSafely` will return false.
For the first invocation in LLD_IN_TEST=2 mode, `inTestOutputDisabled`
is true and lld will not write to stdout/stderr, making many tests fail.
(This essentially discourages `Fatal` calls in the source code.)
Add XFAIL: main-run-twice to these tests similar to
https://reviews.llvm.org/D112898 for Mach-O
```
comment="This test intentionally checks for fatal errors, and fatal errors aren't supported for testing when main is run twice."
xargs </tmp/0 sed -Ei "1s/(;|#|\/\/) REQUIRES: .*/\0\n\1 "$comment"\n\1 XFAIL: main-run-twice/;t;1s/^/# "$comment"\n# XFAIL: main-run-twice\n/"
```
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