[CI] Build ninja on Linux Docker CI builds

[Kobzol]

I want to test if/how much using ninja instead of make speeds up try/dist Linux CI builds. They rebuild LLVM several times, so it could be worth it.

[rust-highfive]

r? @pietroalbini

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[Kobzol]

r? @Mark-Simulacrum

@bors try

[bors]

⌛ Trying commit 95efb00 with merge 0e42a59c953047a7e00c8e17cfc869f49ebf7a68...

[Kobzol]

@bors try-

[Kobzol]

@bors try

[bors]

⌛ Trying commit 31cb150 with merge 94cb68b0f11cd9dbcdbd2e129b5304d6ce471ae4...

[bors]

☀️ Try build successful - checks-actions
Build commit: 94cb68b0f11cd9dbcdbd2e129b5304d6ce471ae4 (94cb68b0f11cd9dbcdbd2e129b5304d6ce471ae4)

[Kobzol]

Ninja is now built in Docker. Now let's see what happens if we actually enable it. For reference, lately dist times have been in the range 1h 20 min - 1h 40 min.

@bors try

[bors]

⌛ Trying commit 139f3bc with merge 413fdf1cf42db425f2245b8b2b6ca43031ce75d6...

[bors]

☀️ Try build successful - checks-actions
Build commit: 413fdf1cf42db425f2245b8b2b6ca43031ce75d6 (413fdf1cf42db425f2245b8b2b6ca43031ce75d6)

[Kobzol]

It seems that building with ninja is actually slower on CI (it took ~2 hours to build).

[Kobzol]

@bors try

[bors]

⌛ Trying commit 139f3bc with merge 572ba4359edc03a746e930674acaf1b3752844d8...

[bors]

☀️ Try build successful - checks-actions
Build commit: 572ba4359edc03a746e930674acaf1b3752844d8 (572ba4359edc03a746e930674acaf1b3752844d8)

[Kobzol]

I was a bit pessimistic towards ninja before, as I didn't realize that the sccache wasn't primed, so the build was slower. But anyways the build is not faster with ninja, it's on par with make. So this is not worth it.