Use go:linkname to access build.Default and modify Compiler in init function. This is much simpler than patching defaultContext() and all its dependencies. - Reduced from 137 lines to 27 lines - Removed zcgo.go (no longer needed) - Removed complex parseGoVersion, defaultContext, and helper functions - Now just sets build.Default.Compiler = "gc" in init() Generated with [codeagent](https://github.com/qbox/codeagent) Co-authored-by: luoliwoshang <luoliwoshang@users.noreply.github.com>