CI: use lld linker on ubuntu

Try lld linker on Ubuntu builds. We may see some improvement on build time.

Note: I had to use clang as well

Note: I also fixed a compilation issue between OSSIM 2.2.0 and clang: addition of using std::nullptr_t in a few places.

added 3 commits

• 915bc6b4 - CI: use new configuration for llvm toolchain (clang+ lld)
• 6e952a55 - CI: remove shark version, wrong version anyway
• 48c3bc29 - CI: try llvm toolchain

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changed the description

Compilation error with ... OSSIM, I may have to fix it like we did before with ITK patches.

added 1 commit

• 7950785f - COMP: fix nullptr_t issue in OSSIM 2.2.0 with clang

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added 1 commit

• e6b23cff - COMP: more nullptr_t issues

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Time results on last pipeline:

• GCC + Shark=OFF : 27min
• Clang + LLD + Shark=ON : 21min

changed the description

merged

mentioned in commit 0f372bfe

added ci label

changed milestone to %7.0.0