go1.14 cgo on windows doesn't link, undefined references to __errno in errno_itself

[glycerine]

building https://github.com/glycerine/goq on windows under go1.13.8 works fine.

under go1.14 I get link failure.

~/go/src/github.com/glycerine/goq
$ go version
go version go1.13.8 windows/amd64

~/go/src/github.com/glycerine/goq
$ go install

~/go/src/github.com/glycerine/goq ## so compile and link worked fine under go1.13.8
$ go1.14 install
# github.com/glycerine/goq
C:\Users\Administrator\sdk\go1.14\pkg\tool\windows_amd64\link.exe: running gcc failed: exit status 1
C:\cygwin64\tmp\go-link-118756859\000001.o: In function `errno_itself':
C:\Users\Administrator\go\src\github.com\glycerine\goq/inspecterrno.go:8: undefined reference to `__errno'
C:\cygwin64\tmp\go-link-118756859\000001.o: In function `addr_of_errno':
C:\Users\Administrator\go\src\github.com\glycerine\goq/inspecterrno.go:5: undefined reference to `__errno'
C:\cygwin64\tmp\go-link-118756859\000001.o: In function `errno_itself':
C:\Users\Administrator\go\src\github.com\glycerine\goq/inspecterrno.go:8: undefined reference to `__errno'
C:\cygwin64\tmp\go-link-118756859\000001.o: In function `addr_of_errno':
C:\Users\Administrator\go\src\github.com\glycerine\goq/inspecterrno.go:5: undefined reference to `__errno'
collect2.exe: error: ld returned 1 exit status

~/go/src/github.com/glycerine/goq

$ gcc --version
gcc.exe (tdm64-1) 5.1.0
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


 ~/go/src/github.com/glycerine/goq
$ which gcc
/cygdrive/c/TDMGCC64/bin/gcc  ## using https://tdm-gcc.tdragon.net/

edit: exactly the same failure under gcc v8.1
/cygdrive/c/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/gcc from https://sourceforge.net/projects/mingw-w64/

[AlexRouSg]

Unable to reproduce with go version go1.14 windows/amd64 and gcc.exe (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 8.1.0

Try cleaning the build cache (go clean -cache) and/or not running in cygwin

[glycerine]

I think go clean -cache fixed it. Why would that be?

[AlexRouSg]

Could be a bug with the build cache, but to find that out would require a way to repo reliability and without changing GCC. As the cache is already known to not detect changes to external C/C++ headers and libs. (#24355)

[glycerine]

okay, sounds like a known issue.