builder,loader: fix -ldflags -X not overriding variables with default values

When a string variable already had a source-level default value, the -ldflags
"-X" flag was silently ignored and the variable remained the default value
at runtime.

Fix by stripping the InitOrder entry for each -X variable before
LoadSSA() is called. With no entry in InitOrder, go/ssa emits no init
store, so the global stays zero-valued in the IR. makeGlobalsModule
still injects the actual -X values at final link time.

The -X values remain out of the per-package build cache with only the
variable names appearing in the cache key.

Signed-off-by: deadprogram <ron@hybridgroup.com>

main_test.go

@@ -155,6 +155,19 @@ func TestBuild(t *testing.T) {
 			}
 			runTestWithConfig("ldflags.go", t, opts, nil, nil)
 		})
+
+		// Same as ldflags, but the global has a default value in source.
+		// -ldflags -X must override it, matching standard Go behaviour.
+		t.Run("ldflags-initialized", func(t *testing.T) {
+			t.Parallel()
+			opts := optionsFromTarget("", sema)
+			opts.GlobalValues = map[string]map[string]string{
+				"main": {
+					"someGlobal": "foobar",
+				},
+			}
+			runTestWithConfig("ldflags-initialized.go", t, opts, nil, nil)
+		})
 	})
 
 	if testing.Short() {