Add option for -Wl,--gdb-index and update documentation
This seems fine. I have -DCMAKE_EXE_LINKER_FLAGS=-Wl,--gdb-index -DCMAKE_SHARED_LINKER_FLAGS=-Wl,--gdb-index -DLLVM_USE_SPLIT_DWARF=On in my long cmake command line. I am just wondering whether this new option will be discoverable.
Some people don't use -DLLVM_USE_LINKER=lld, but use -DLLVM_ENABLE_LLD=On.
It's a bit confusing, but earlier in HandleLLVMOptions.cmake, LLVM_ENABLE_LLD is normalized into LLVM_USE_LINKER. There's also an internal variable LINKER_IS_LLD_LINK that is set by either.
Oops, I saw your patch to LLVM_USE_SPLIT_DWARF that landed, but missed that one.
It seems like -fuse-ld=gold/lld would be the simplest way forward? Do you plan to revise your patch to address that, lld, and @smeenai comment about -ggnu-pubnames? My only other feedback would be to update the docs, since even LLVM_USE_SPLIT_DWARF isn't currently listed, and that incorporating objcopy would make things more complicated.
Perhaps that issue should be fixed (so that LLVM_ENABLE_LLD/LLVM_USE_LINKER kicks in early enough (same as putting -fuse-ld in CMAKE_EXE_LINKER_FLAGS) - seems a bit problematic to have different compilation modes at different points along that (but I guess make those LLD/linker enabling features are designed to use make detection to silently not do the thing you asked for if it's unsupported)
To my mind this all seems a bit complicated - and I wonder what the point of all these cmake supported features is compared to users specifying the flags in the flag variables directly?