Support mold linker

[yixinglu]

What type of PR is this?

• bug
• feature
• enhancement

What problem(s) does this PR solve?

Issue(s) number:

Description:

use the mold linker to speed up nebula compilation:

1. download the mold linker from the release page and decompress the tar to your $PATH directory, such as $HOME/.local by
   tar zxf mold-1.10.1-x86_64-linux.tar.gz --strip-components=1 -C $HOME/.local/
2. enter the nebula repo build directory
3. specify the NEBULA_USE_LINKER variable when you configure the cmake:

   cmake -DNEBULA_USE_LINKER=mold ..
   

4. happy to build nebula now

How do you solve it?

Special notes for your reviewer, ex. impact of this fix, design document, etc:

Checklist:

Tests:

• Unit test(positive and negative cases)
• Function test
• Performance test
• N/A

Affects:

• Documentation affected (Please add the label if documentation needs to be modified.)
• Incompatibility (If it breaks the compatibility, please describe it and add the label.）
• If it's needed to cherry-pick (If cherry-pick to some branches is required, please label the destination version(s).)
• Performance impacted: Consumes more CPU/Memory

Release notes:

Please confirm whether to be reflected in release notes and how to describe:

ex. Fixed the bug .....

[dutor]

Bravo.