how to debug go build errors

[Martin Sebor]

Hi Ian,

While testing what should be an innocuous patch to add LTO
to a bunch of middle-end warning options

   https://gcc.gnu.org/ml/gcc-patches/2018-02/msg00381.html

I get Go errors during ordinary bootstrap about undefined names
for errno constants:

/opt/notnfs/msebor/src/gcc/84212/libgo/go/syscall/env_unix.go:96:10: 
error: reference to undefined name ‘EINVAL’

Bootstrapping all other front ends (including Ada and Brig),
succeeds and there are no regressions in the test suite.

I have no experience with Go.  Does anything about the patch
jump out at you that could be causing this?  If not, can you
suggest how to debug it?

Thanks
Martin