cmd/link: only add dummy XCOFF reference if the symbol exists
On AIX when external linking, for some symbols we need to add
dummy references to prevent the external linker from discarding
them. Currently we add the reference unconditionally. But if the
symbol doesn't exist, the linking fails in a later stage for
generating external relocation of a nonexistent symbol. The
symbols are special symbols that almost always exist, except that
go:buildid may not exist if the linker is invoked without the
-buildid flag. The go command invokes the linker with the flag, so
this can only happen with manual linker invocation. Specifically,
test/run.go does this in some cases.
Fix this by checking the symbol existence before adding the
reference. Re-enable tests on AIX.
Perhaps the linker should always emit a dummy buildid even if the
flag is not set...
Fixes #54814.
Change-Id: I43d81587151595309e189e38960cbda9a1c5ca32
Reviewed-on: https://go-review.googlesource.com/c/go/+/427620
Run-TryBot: Cherry Mui <cherryyz@google.com> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Than McIntosh <thanm@google.com>