cmd/link: fix SCONST symbol handling on darwin

Don't include SCONST symbols in the symbol table when
NotInSymbolTable is set. This is what the old code (genasmsym)
does.

In fact, SCONST symbol is only emitted by the field tracking
code, and is always NotInSymbolTable. So we should just not
include them at all, or not generate SCONST symbols at all. But
at this late stage I'll just restore the old behavior.

Change-Id: If6843003e16701d45b8c67b2297098a7babdec52
Reviewed-on: https://go-review.googlesource.com/c/go/+/233997
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -798,7 +798,7 @@ func collectmachosyms(ctxt *Link) {
 			continue
 		}
 		t := ldr.SymType(s)
-		if t >= sym.SELFRXSECT && t < sym.SXREF { // data sections handled in dodata
+		if t >= sym.SELFRXSECT && t < sym.SXREF || t == sym.SCONST { // data sections handled in dodata
 			if t == sym.STLSBSS {
 				// TLSBSS is not used on darwin. See data.go:allocateDataSections
 				continue
@@ -810,7 +810,7 @@ func collectmachosyms(ctxt *Link) {
 		}
 
 		switch t {
-		case sym.SDYNIMPORT, sym.SHOSTOBJ, sym.SUNDEFEXT, sym.SCONST:
+		case sym.SDYNIMPORT, sym.SHOSTOBJ, sym.SUNDEFEXT:
 			addsym(s)
 		}