Support raw-dylib link kind on ELF

[Noratrieb]

raw-dylib is a link kind that allows rustc to link against a library without having any library files present.
This currently only exists on Windows. rustc will take all the symbols from raw-dylib link blocks and put them in an import library, where they can then be resolved by the linker.

While import libraries don't exist on ELF, it would still be convenient to have this same functionality. Not having the libraries present at build-time can be convenient for several reasons, especially cross-compilation. With raw-dylib, code linking against a library can be cross-compiled without needing to have these libraries available on the build machine. If the libc crate makes use of this, it would allow cross-compilation without having any libc available on the build machine. This is not yet possible with this implementation, at least against libc's like glibc that use symbol versioning. The raw-dylib kind could be extended with support for symbol versioning in the future.

This implementation is very experimental and I have not tested it very well. I have tested it for a toy example and the lz4-sys crate, where it was able to successfully link a binary despite not having a corresponding library at build-time.

I was inspired by Björn's comments in https://internals.rust-lang.org/t/bundle-zig-cc-in-rustup-by-default/22096/27
Tracking issue: #135694

r? bjorn3

try-job: aarch64-apple
try-job: x86_64-msvc-1
try-job: x86_64-msvc-2
try-job: test-various

[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

Some changes occurred in src/tools/compiletest

cc @jieyouxu

[jieyouxu]

compiletest changes LGTM, would be great if you could add the two new directives to the directives listing in r-d-g

[jieyouxu]

@bors p=5 (rollup scheduling)

[tgross35]

Since this is iffy and next in queue, could it get rolled up with a few alwayses? That seems reasonable for all the iffys (otherwise they would be nevers, we're no worse off an iffy fails)

[jieyouxu]

Yeah that would work. That's why iffy exists in the first place.

[jieyouxu]

@bors p=0 (to be included in another rollup)

[bors]

⌛ Testing commit a954c51 with merge 161f78c...

[bors]

💔 Test failed - checks-actions

[Kobzol]

@bors retry network error

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

##[endgroup]
Image input checksum bed9166b5ea6c475a5e82dbd59d7a7df1d5cefd4eaf9cdd5ef976d511c06a59516a0dd9789681ba52d63a18529eaaa52a26a746c004596ee9e5d584a3b2de811
##[group]Building docker image for dist-android
Docker version 26.1.3, build b72abbb
Error response from daemon: Get "https://ghcr.io/v2/": Get "https://ghcr.io/token?account=rust-lang-ci&client_id=docker&offline_token=true&service=ghcr.io": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)
##[error]Process completed with exit code 1.

[bors]

⌛ Testing commit a954c51 with merge 6d088a8...

[bors]

💔 Test failed - checks-actions

[Kobzol]

@bors retry network error

sigh..

[bors]

⌛ Testing commit a954c51 with merge 5f802db...

[bors]

💔 Test failed - checks-actions

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[Noratrieb]

@bors retry
@bors treeclosed ghcr network errors

[Noratrieb]

@bors treeclosed=100

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[bors]

⌛ Testing commit a954c51 with merge f9e0239...

[bors]

☀️ Test successful - checks-actions
Approved by: bjorn3
Pushing f9e0239 to master...

[rust-timer]

Finished benchmarking commit (f9e0239): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary -1.5%, secondary 0.8%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.5%	[2.1%, 3.0%]	2
Improvements ✅ (primary)	-1.5%	[-1.5%, -1.5%]	1
Improvements ✅ (secondary)	-2.5%	[-2.5%, -2.5%]	1
All ❌✅ (primary)	-1.5%	[-1.5%, -1.5%]	1

Cycles

Results (secondary -6.3%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.3%	[-6.4%, -6.2%]	2
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: missing data
Artifact size: 362.04 MiB -> 362.05 MiB (0.00%)