ELF: Emit (most) instantiated symbols in COMDATs

[kinke]

No description provided.

[ljmf00-wekaio]

I don't think this works, I'll double confirm on weka source code, but we have been getting too much linker issues by applying COMDAT to most of the symbols. e.g.:

ld.lld: error: relocation refers to a discarded section: .text._D5mecca3lib10reflection__T2asVAyaa13_6e6f7468726f7720406e6f6763TDFNaNbNiNfZvZQBzFNcMQuZ9__lambda2MFNaNbNiNeZQBs
>>> defined in core/3rdparty/build/mecca/libmecca-notrace.a(.._.._mecca_src_mecca_lib_exception.d.o)
>>> section group signature: _D5mecca3lib10reflection__T2asVAyaa13_6e6f7468726f7720406e6f6763TDFNaNbNiNfZvZQBzFNcMQuZ9__lambda2MFNaNbNiNeZQBs
>>> prevailing definition is in core/3rdparty/build/mecca/libmecca-notrace.a(.._.._mecca_src_mecca_reactor_io_inotify.d.o)
>>> referenced by reflection.d:556 (../core/3rdparty/mecca/src/mecca/lib/reflection.d:556)
>>>               .._.._mecca_src_mecca_lib_exception.d.o:(_D5mecca3lib9exception6ExcBuf__T15constructHelperHTC4coreQBt11AssertErrorTAyaZQBuMFNbNiNeQpmbKQuZQBu) in archive core/3rdparty/build/mecca/libmecca-notrace.a

This verifies on symbols with InternalLinkage and only after upgrading the compiler (symbols with internal linkage are the ones that are relocations to discarded symbols). I haven't tested with the same LLVM version tho, could be an upstream regression.

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Bottom line: weka@e1cca7a with --enable-wekamods=true yields this linker error, and, without the mods, data culling doesn't work (we start to get duplicate sections, as described in the issue). The --enable-wekamods=true works on older versions. So we are on this middle ground where none works unless we only mark specific linkage with comdat.

I'll try to create a test to demonstrate this.

[ljmf00-wekaio]

Tested, and it works! I see, this works if we guarantee that templateLinkage is not ever InternalLinkage, which probably is just a derivative of _odr attributes? What about --fvisibility=hidden, this doesn't influence templateLinkage, right? If that's all true, I'm good with this change.

[kinke]

templateLinkage is always an ODR linkage:

ldc/driver/main.cpp

Lines 470 to 472 in 580ff68

	templateLinkage = global.params.linkonceTemplates == LinkonceTemplates::no
	? LLGlobalValue::WeakODRLinkage
	: LLGlobalValue::LinkOnceODRLinkage;