build: always use strings for compiler version in gyp files

If GYP finds a string variable that can be converted to an integer,
it will do it when the variable is expanded. Use "0.0" instead of "0"
to force strings and be able to use comparison operations such as
`gas_version >= "2.26"` in Python 3.

PR-URL: https://github.com/nodejs/node/pull/29897


Reviewed-By: Christian Clauss <cclauss@me.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>