Add support for LLVM 19

[aykevl]

This is incomplete. I've only made this so that we have a LLVM 19 branch ready to go once LLVM 19 is released (and the Xtensa fork has been rebased).

I will make a new PR once it is ready.

Some things that need to be resolved:

• LLVM 19 needs to be released (probably early September)
• Homebrew needs to be updated (see WIP use LLVM 19 go-llvm#65 and llvm 19.1.0 Homebrew/homebrew-core#181351)
• libLLVM-19.so is a broken symbolic link llvm/llvm-project#105987 needs to be fixed, or we need to use a hacky workaround.
• The Xtensa fork needs to be rebased (though we can probably have partial LLVM 19 support before then for distro maintainers).

[github-actions]

Size difference with the dev branch:

Binary size difference

not the same command!
    tinygo build -size short -o ./build/test.bin -target=m5stamp-c3          ./examples/ws2812
    '-xesppie' is not a recognized feature for this target (ignoring feature)
 flash                          ram
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 263712  263408   -304  -0.12%   46748   46748      0   0.00% tinygo build -size short -o ./build/test.hex -target=pyportal ./examples/ili9341/slideshow
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  69304   69232    -72  -0.10%    6968    6968      0   0.00% tinygo build -size short -o ./build/test.hex -target=itsybitsy-m0 ./examples/flash/console/spi
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  11884   11836    -48  -0.40%    6580    6580      0   0.00% tinygo build -size short -o ./build/test.hex -target=nano-33-ble ./examples/apds9960/proximity/main.go
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   5764    5772      8   0.14%    9522    9522      0   0.00% tinygo build -size short -o ./build/test.bin -target=m5stamp-c3          ./examples/ws2812
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  11732   11764     32   0.27%    4780    4780      0   0.00% tinygo build -size short -o ./build/test.hex -target=circuitplay-express ./examples/lis3dh/main.go
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[deadprogram]

LLVM 19 is out and the default for homebrew installs: https://formulae.brew.sh/formula/llvm

[aykevl]

Yes. But it should continue to work, if people install LLVM as brew install llvm@18 (as IIRC it says in the documentation).

I can make a PR to support LLVM 19 for go install only if needed, but I'd prefer to do that only when needed (it is extra work to make and test). Instead, I'd prefer to wait until Espressif releases their LLVM 19 fork.

[QuLogic]

I noticed with lld 19 that several experimental flags warn that they don't exist and are being ignored. As this changes those to the non-prefixed versions, doesn't that mean that lld 18 will now warn that those don't exist and start ignoring them? In other words, don't we need some translation for -experimental--prefixed features between >=19 and <19?

[aykevl]

I noticed with lld 19 that several experimental flags warn that they don't exist and are being ignored. As this changes those to the non-prefixed versions, doesn't that mean that lld 18 will now warn that those don't exist and start ignoring them? In other words, don't we need some translation for -experimental--prefixed features between >=19 and <19?

These flags often change with LLVM releases, especially for RISC-V. So far it hasn't been breaking anything to use the flags of a different LLVM release, but the warnings are kinda ugly.
One solution would be to use a different set of flags for different LLVM versions, though I don't really like to maintain those. It's a solution though if needed.

(To be clear: these warnings only happen when using a LLVM version that's not the "primary"/latest supported LLVM version. Most users shouldn't see those).

[aykevl]

In other news, I've updated this PR since the Xtensa fork got updated with LLVM 19 support!

[deadprogram]

At last! Thanks for all the work on this @aykevl now merging.