Add an order-only dependency on the build number file

Remote execution and other tools can be confused by references to
build_number.txt without a dependency.  Add an order-only dependency,
which maintains the current behavior.

Test: BUILD_NUMBER=1 && m aapt && aapt version # shows 1
      BUILD_NUMBER=2 && m aapt && aapt version # shows 1
      rm out/soong/.intermediates/frameworks/base/tools/aapt/aapt/linux_glibc_x86_64/aapt
      BUILD_NUMBER=2 && m aapt && aapt version # shows 2
Change-Id: Icfa98d6840b1dc2e273ba29c33011635d1cf93b1

cc/linker.go

@@ -501,19 +501,21 @@ func init() {
 var injectVersionSymbol = pctx.AndroidStaticRule("injectVersionSymbol",
 	blueprint.RuleParams{
 		Command: "$symbolInjectCmd -i $in -o $out -s soong_build_number " +
-			"-from 'SOONG BUILD NUMBER PLACEHOLDER' -v $buildNumberFromFile",
+			"-from 'SOONG BUILD NUMBER PLACEHOLDER' -v $$(cat $buildNumberFile)",
 		CommandDeps: []string{"$symbolInjectCmd"},
 	},
-	"buildNumberFromFile")
+	"buildNumberFile")
 
 func (linker *baseLinker) injectVersionSymbol(ctx ModuleContext, in android.Path, out android.WritablePath) {
+	buildNumberFile := ctx.Config().BuildNumberFile(ctx)
 	ctx.Build(pctx, android.BuildParams{
 		Rule:        injectVersionSymbol,
 		Description: "inject version symbol",
 		Input:       in,
 		Output:      out,
+		OrderOnly:   android.Paths{buildNumberFile},
 		Args: map[string]string{
-			"buildNumberFromFile": proptools.NinjaEscape(ctx.Config().BuildNumberFromFile()),
+			"buildNumberFile": buildNumberFile.String(),
 		},
 	})
 }