I started to copy the Go 1.7 interface code, but the gc and gccgo
representations of interfaces are too different. So instead I rewrote
the gccgo interface code from C to Go. The code is largely the same as
it was, but the names are more like those used in the gc runtime.
I also copied over the string comparison functions, and tweaked the
compiler to use eqstring when comparing strings for equality.
Reviewed-on: https://go-review.googlesource.com/31591
From-SVN: r241384
6b752cfac4