[Bug go/101246] New: gccgo cross-compiler targeting arm fails to build with gcc 11. Missing structs in runtime.inc. Using uclibc-ng

["lancethepants at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101246

            Bug ID: 101246
           Summary: gccgo cross-compiler targeting arm fails to build with
                    gcc 11. Missing structs in runtime.inc. Using
                    uclibc-ng
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: go
          Assignee: ian at airs dot com
          Reporter: lancethepants at gmail dot com
                CC: cmang at google dot com
  Target Milestone: ---

I've recently run into an issue building a go cross-compiler on x86_64
targeting an arm embedded device (Netgear R7000 router) starting with gcc 11.

I was previously able to build the cross-compiler (c,c++,go) under gcc 9 & 10,
but am getting the errors listed at the bottom.

armv7 cortexa9 cpu (no fpu)
uclibc-ng (latest)
kernel 2.6.36.4.

I don't think the old kernel is an issue because the same errors arise if I use
kernel 5.12.  

I tried building with glibc, and it does work then. So I think the issue is
with uclibc-ng.

So I did use uclibc-ng with gcc 9 & 10 with success, but for some reason with
gcc 11 I am now running into this issue.

My untrained eyes think it may be as easy as a couple missing structs within
runtime.inc.   Is runtime.inc generated? because it doesn't appear in
unconfigured source I've notices.

thanks,
Lance

Build Errors
In file included from ../../../libgo/runtime/runtime.h:105,
                  from ../../../libgo/runtime/go-main.c:17:
./runtime.inc:1357:29: error: field ‘__state’ has incomplete type
  1357 |         struct ___mbstate_t __state;
       |                             ^~~~~~~
./runtime.inc:1360:33: error: field ‘__lock’ has incomplete type
  1360 |         struct _pthread_mutex_t __lock;
       |