build llvm in //libs/jsruntime/build.rs

[masnagam]

currently, we build llvm before running cargo commands. this was an easier way but there are the following disadvantages:

• llvm is built w/ specific options
  • we cannot change options in accordance with the build profile to use
  • LLVM_USE_PERF, LLVM_USE_SANITIZER, etc.
• we have to build it manually before running cargo commands

change //libs/jsruntime/build.rs and specify build options according to the build profile. we can use the cmake crate for building c++ bridge files together with llvm.

[masnagam]

this is another story, but using the shared library (libLLVM.so) may improve disk usage. currently, the binaries generated by make [build|test|bench] consume tens of GB.