Update build tags for static link

[2dvorak]

Proposed changes

• This PR adds build tags for building statically linked kaia binaries
  • Some glibc features (e.g., libnss) can cause dependencies on specific version of glibc.
  • To avoid using such features, we can add build tags to guide go compiler (and linker) to use Golang implementation (as an alternative to the related glibc feature)
  • This is a known issue in Golang, and also a mitigation adopted in geth

The following build method now produces a fully static binary.

KAIA_STATIC_LINK=1 make ken

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