Fix compilation issues of bcc on Alibaba Cloud Linux 3

[suxb201]

When trying to compile bcc on Alibaba Cloud Linux 3, I found several issues that I've fixed in this PR:

• LLVM10 Compilation: Alibaba Cloud Linux 3 is compatible with CentOS 8 and does not support epel-release and centos-release-scl. This means we need to manually compile llvm10.
• Clang Search Directory: There was a problem with the search directory for clang. I've added /usr/local/lib/ to fix this.
• Python Environment with Conda: I use conda to manage my Python environment. I found that bcc would install to /usr/lib/python3.9/site-packages/ by default, not /root/miniconda3/lib/python3.9/site-packages/. By removing the --prefix argument, bcc now installs correctly in different environments. Without this change, bcc would end up in the wrong Python directory and using python setup.py install --prefix " ".

I appreciate any review and feedback.