### What problem were solved in this pull request?

Issue Number: close #247 

Problem:
Compile miniob with static gcc and g++ failed while there is no static
gcc library on rockylinux.

### What is changed and how it works?
Add cmake option static_stdlib with default value off.
In normal case, we compile miniob and run/debug it on the same machine,
so dynamic linking works fun. If we want to move observer binary to
other machine and test, we can recompile miniob with static_stdlib ON.