Merge in functionality from RNP's GPG build script

[ronaldtse]

https://github.com/riboseinc/rnp/blob/6fa0c09fa94168206aa2df617287d9f8a7fba5df/ci/install.sh#L67

build_gpg_stable/build_gpg_beta are functions that the RNP build script uses to install GPG.

@skalee can you help check the code to see if any functionality we can merge in from there? Thanks.

And the combination of this:

  if [ "$GPG_VERSION" = "stable" ]; then
    #                npth libgpg-error libgcrypt libassuan libksba pinentry gnupg
    build_gpg_stable 1.5  1.31         1.8.2     2.5.1     1.3.5   1.1.0    2.2.7
  elif [ "$GPG_VERSION" = "beta" ]; then
    #              gettext npth libgpg-error libgcrypt libassuan libksba pinentry gnupg
    build_gpg_beta latest master master master master master master fe621cc

[ronaldtse]

@skalee could you help integrate this script in https://github.com/riboseinc/rnp/issues/690 in the RNP repo? Thanks!