Go 1.3 offers many changes and improvements throughout, Godoc static analysis support, GC supports Native Client execution sandbox on 32-bit/64-bit x86 architectures, and experimental support for new operating systems. Those unfamiliar with last month's release of Go 1.3 can read more via the release notes. There's also other commentary about the Go 1.3 language update via the Go Blog.
Hitting mainline GCC today is libgo for Go 1.3. The Go updates and many other changes will be part of the GCC 4.10 release to happen in 2015.