variable: Update product_variables.arc struct

- Add whole_static_libs
- Add `android:"arch_variant"` so arc struct can be used inside
  target.android.product_variables

Test: m
Bug: 171847983
Change-Id: Iaa99b007302462ef66d0d943bc16d37a6e8ecdc7
diff --git a/android/variable.go b/android/variable.go
index 93dac3d..753ddd7 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -126,13 +126,14 @@
 		}
 
 		Arc struct {
-			Cflags       []string
-			Exclude_srcs []string
-			Include_dirs []string
-			Shared_libs  []string
-			Static_libs  []string
-			Srcs         []string
-		}
+			Cflags            []string `android:"arch_variant"`
+			Exclude_srcs      []string `android:"arch_variant"`
+			Include_dirs      []string `android:"arch_variant"`
+			Shared_libs       []string `android:"arch_variant"`
+			Static_libs       []string `android:"arch_variant"`
+			Srcs              []string `android:"arch_variant"`
+			Whole_static_libs []string `android:"arch_variant"`
+		} `android:"arch_variant"`
 
 		Flatten_apex struct {
 			Enabled *bool