Revert "Restrict COFF to a single thread when symbol count is high (#50874)"

[topolarity]

This reverts commit eb4416b.

As of LLVM 16, we automatically emit:

.drectve `-exclude-symbols:"<symbol>"`

which mitigates this issue where it is supported by the linker (GCC 11+ and LLD 14+ are tested working)

PackageCompiler on Windows now ships GCC 14 (JuliaLang/PackageCompiler.jl#1012), so we should no longer need this workaround that can make a 15-minute sysimage compilation take an hour+

[DilumAluthge]

So, with this reversion, PackageCompiler will have a new GCC version requirement (GCC 11+), right? Does that requirement only apply to Windows, or does it also apply to Linux and maCOS?

[topolarity]

PackageCompiler will have a new GCC version requirement (GCC 11+), right?

Yes - slightly older might be OK too, but GCC 8 is definitely not supported. It spits out:

Warning: .drectve `-exclude-symbols:jl_fvar_count_9 ' unrecognized
Warning: .drectve `-exclude-symbols:jl_fvar_ptrs_9 ' unrecognized
Warning: .drectve `-exclude-symbols:jl_clone_slots_9 ' unrecognized
Warning: .drectve `-exclude-symbols:jl_clone_idxs_9 ' unrecognized

when used on Julia 1.11+ (JuliaLang/PackageCompiler.jl#918)

Does that requirement only apply to Windows, or does it also apply to Linux and maCOS?

It should only apply to Windows / COFF (where we rely on these directives)

[DilumAluthge]

SGTM. We bundle the gcc on Windows. In theory people could override with their own gcc, so in theory we should document the Windows-specfici gcc 11+ requirement somewhere. But most people will use the bundled gcc on Windows, so it's not super pressing to add the docs.