cmd/cgo: fails to parse object file generated by clang -flto

[ianlancetaylor]

On tip, on linux-amd64, in the misc/swig/callback directory, running this command

CC=clang CGO_CFLAGS="-g -O2 -flto" CGO_LDFLAGS="-flto" go test -v

fails as follows:

# misc/swig/callback
cgo: cannot parse gcc output $WORK/b059//_cgo_.o as ELF, Mach-O, PE, XCOFF object
FAIL	misc/swig/callback [build failed]

At least when using clang, cgo has to disable -flto when it compiles the object, because cgo is unable to parse the byte code generated by clang.

[MrQubo]

Same with gcc.

[MrQubo]

Might be a duplicate of #43505.

[gopherbot]

Change https://golang.org/cl/322614 mentions this issue: cmd/link, cmd/cgo: support -flto in CFLAGS

[gopherbot]

Change https://golang.org/cl/324049 mentions this issue: cmd/link: move issue 43830 tests out of TestScript