cmd/link: change -strictdups checking to handle mix of flags

Update the recently-added '-strictdups' sanity checking to avoid
failing the link in cases where we have objects feeding into the link
with a mix of command line flags (and in particular some with "-N" and
some without). This scenario will trigger errors/warnings due to
inlinable functions and wrapper functions that have different sizes
due to presence or lack of optimization.

Update #31034.

Change-Id: I1dd9e37c2f9bea5da0ab82e32e6fc210aebf6a65
Reviewed-on: https://go-review.googlesource.com/c/go/+/169160
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/link/internal/ld/main.go

@@ -148,6 +148,7 @@ func Main(arch *sys.Arch, theArch Arch) {
 	if objabi.Fieldtrack_enabled != 0 {
 		ctxt.Reachparent = make(map[*sym.Symbol]*sym.Symbol)
 	}
+	checkStrictDups = *FlagStrictDups
 
 	startProfile()
 	if ctxt.BuildMode == BuildModeUnset {