[dev.link] cmd/link: process cgo_import_static before host object loading

In internal linking mode, we need to process cgo_import_static
directives before loading host objects, because the directive is
to tell the host object loader how to deal with imported symbols.

This should fix linking with old object files. I think there
needs some similar logic for new object files, but I'll leave
that for later.

Change-Id: Icaa286de626ea1876086dbdd015047084c92caf9
Reviewed-on: https://go-review.googlesource.com/c/go/+/204697
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

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

@@ -443,20 +443,6 @@ func (ctxt *Link) loadlib() {
 		}
 	}
 
-	// Conditionally load host objects, or setup for external linking.
-	hostobjs(ctxt)
-	hostlinksetup(ctxt)
-
-	if *flagNewobj {
-		// Add references of externally defined symbols.
-		ctxt.loader.LoadRefs(ctxt.Arch, ctxt.Syms)
-	}
-
-	// Now that we know the link mode, set the dynexp list.
-	if !*flagNewobj { // set this later in newobj mode
-		setupdynexp(ctxt)
-	}
-
 	if ctxt.LinkMode == LinkInternal && len(hostobj) != 0 {
 		// Drop all the cgo_import_static declarations.
 		// Turns out we won't be needing them.
@@ -473,7 +459,23 @@ func (ctxt *Link) loadlib() {
 				}
 			}
 		}
+	}
 
+	// Conditionally load host objects, or setup for external linking.
+	hostobjs(ctxt)
+	hostlinksetup(ctxt)
+
+	if *flagNewobj {
+		// Add references of externally defined symbols.
+		ctxt.loader.LoadRefs(ctxt.Arch, ctxt.Syms)
+	}
+
+	// Now that we know the link mode, set the dynexp list.
+	if !*flagNewobj { // set this later in newobj mode
+		setupdynexp(ctxt)
+	}
+
+	if ctxt.LinkMode == LinkInternal && len(hostobj) != 0 {
 		// If we have any undefined symbols in external
 		// objects, try to read them from the libgcc file.
 		any := false