rustc: Support auto-retry linking on a segfault

This is a last-ditch attempt to help our pain with dealing with #38878 on the
bots. A new environment variable is added to the compiler,
`RUSTC_RETRY_LINKER_ON_SEGFAULT`, which will instruct the compiler to
automatically retry the final linker invocation if it looks like the linker
segfaulted (up to 2 extra times).

Unfortunately there have been no successful attempts to debug #38878. The only
information seems to be that the linker (e.g. `ld` on OSX) is segfaulting
somewhere in some thread pool implementation. This appears to be spurious as
failed PRs will later merge.

The hope is that this helps the queue keep moving without clogging and delaying
PRs due to #38878.

… r=arielb1

rustc: Support auto-retry linking on a segfault

This is a last-ditch attempt to help our pain with dealing with rust-lang#38878 on the
bots. A new environment variable is added to the compiler,
`RUSTC_RETRY_LINKER_ON_SEGFAULT`, which will instruct the compiler to
automatically retry the final linker invocation if it looks like the linker
segfaulted (up to 2 extra times).

Unfortunately there have been no successful attempts to debug rust-lang#38878. The only
information seems to be that the linker (e.g. `ld` on OSX) is segfaulting
somewhere in some thread pool implementation. This appears to be spurious as
failed PRs will later merge.

The hope is that this helps the queue keep moving without clogging and delaying
PRs due to rust-lang#38878.

… r=arielb1

rustc: Support auto-retry linking on a segfault

This is a last-ditch attempt to help our pain with dealing with rust-lang#38878 on the
bots. A new environment variable is added to the compiler,
`RUSTC_RETRY_LINKER_ON_SEGFAULT`, which will instruct the compiler to
automatically retry the final linker invocation if it looks like the linker
segfaulted (up to 2 extra times).

Unfortunately there have been no successful attempts to debug rust-lang#38878. The only
information seems to be that the linker (e.g. `ld` on OSX) is segfaulting
somewhere in some thread pool implementation. This appears to be spurious as
failed PRs will later merge.

The hope is that this helps the queue keep moving without clogging and delaying
PRs due to rust-lang#38878.

… r=arielb1

rustc: Support auto-retry linking on a segfault

This is a last-ditch attempt to help our pain with dealing with rust-lang#38878 on the
bots. A new environment variable is added to the compiler,
`RUSTC_RETRY_LINKER_ON_SEGFAULT`, which will instruct the compiler to
automatically retry the final linker invocation if it looks like the linker
segfaulted (up to 2 extra times).

Unfortunately there have been no successful attempts to debug rust-lang#38878. The only
information seems to be that the linker (e.g. `ld` on OSX) is segfaulting
somewhere in some thread pool implementation. This appears to be spurious as
failed PRs will later merge.

The hope is that this helps the queue keep moving without clogging and delaying
PRs due to rust-lang#38878.

Rollup of 38 pull requests

- Successful merges: #39202, #39820, #39918, #39921, #40092, #40146, #40199, #40225, #40239, #40257, #40259, #40261, #40277, #40278, #40287, #40297, #40311, #40315, #40319, #40324, #40336, #40340, #40344, #40345, #40367, #40369, #40372, #40373, #40379, #40385, #40386, #40389, #40400, #40404, #40410, #40422, #40423, #40424
- Failed merges: #40220, #40329, #40426

rustc: Support auto-retry linking on a segfault

This is a last-ditch attempt to help our pain with dealing with #38878 on the
bots. A new environment variable is added to the compiler,
`RUSTC_RETRY_LINKER_ON_SEGFAULT`, which will instruct the compiler to
automatically retry the final linker invocation if it looks like the linker
segfaulted (up to 2 extra times).

Unfortunately there have been no successful attempts to debug #38878. The only
information seems to be that the linker (e.g. `ld` on OSX) is segfaulting
somewhere in some thread pool implementation. This appears to be spurious as
failed PRs will later merge.

The hope is that this helps the queue keep moving without clogging and delaying
PRs due to #38878.

Rollup of 38 pull requests

- Successful merges: #39202, #39820, #39918, #39921, #40092, #40146, #40199, #40225, #40239, #40257, #40259, #40261, #40277, #40278, #40287, #40297, #40311, #40315, #40319, #40324, #40336, #40340, #40344, #40345, #40367, #40369, #40372, #40373, #40379, #40385, #40386, #40389, #40400, #40404, #40410, #40422, #40423, #40424
- Failed merges: #40220, #40329, #40426

Fix #38878 again — restart linker when seeing SIGBUS in additional to SIGSEGV.

In #45985 (comment) we see a linker crashed due to Bus Error (signal 10) on macOS. The error was not caught by #40422 since the PR only handles Segmentation Fault (signal 11). The crash log indicates the problem is the same as #38878, so we just amend #40422 to include SIGBUS as well.

(Additionally, modified how the crash logs are printed so that irrelevant logs are truly filtered out.)