fix: Link conda lib during CIRCT build

[geekLucian]

I am using FireSim x Chipyard on AWS. Unfortunately, libc on AWS is too old to use firtool installed from conda, so I have to build CIRCT from scratch on AWS.

But during CIRCT build, I got following errors:

/home/centos/chipyard/.conda-env/bin/../lib/gcc/x86_64-conda-linux-gnu/11.4.0/../../../../x86_64-conda-linux-gnu/bin/ld: /home/centos/chipyard/.conda-env/lib/libicuuc.so.73: undefined reference to `std::condition_variable::wait(std::unique_lock<std::mutex>&)@GLIBCXX_3.4.30'

I am sure the conda lib is in LD_LIBRARY_PATH, but cmake building process somehow is linking against the wrong libstdc++.so. Add link flag -DCMAKE_EXE_LINKER_FLAGS="-L$RDIR/.conda-env/lib" to cmake will resolve this. (Not sure if this is the most correct way to do so, but this fix works even if user doesn't have conda env created during build-setup)

Related PRs / Issues:

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

Contributor Checklist:

• Did you set main as the base branch?
• Is this PR's title suitable for inclusion in the changelog and have you added a changelog:<topic> label?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• Did you mark the PR with a changelog: label?
• (If applicable) Did you update the conda .conda-lock.yml file if you updated the conda requirements file?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you add a test demonstrating the PR?

• (If applicable) Did you mark the PR as Please Backport?

[jerryz123]

I think this should be ok.