cmdline property in bootimg can be customized for debuggable builds

This change adds product_variables.debuggable.cmdline so that the kernel
cmdline arguments can be augmented for the debuggable builds.

To support that the type of the property has changed to string array.

Bug: 181936135
Test: inspect build.ninja
Change-Id: I81b3ead5187ccb378efabb87d1d15fbdb59d8e2f
diff --git a/android/variable.go b/android/variable.go
index 5cf9aa8..9d7c1e6 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -108,6 +108,8 @@
 			Static_libs       []string
 			Whole_static_libs []string
 			Shared_libs       []string
+
+			Cmdline []string
 		}
 
 		// eng is true for -eng builds, and can be used to turn on additionaly heavyweight debugging
diff --git a/filesystem/bootimg.go b/filesystem/bootimg.go
index 29a8a39..73d807d 100644
--- a/filesystem/bootimg.go
+++ b/filesystem/bootimg.go
@@ -60,8 +60,8 @@
 	// https://source.android.com/devices/bootloader/partitions/vendor-boot-partitions
 	Vendor_boot *bool
 
-	// Optional kernel commandline
-	Cmdline *string `android:"arch_variant"`
+	// Optional kernel commandline arguments
+	Cmdline []string `android:"arch_variant"`
 
 	// File that contains bootconfig parameters. This can be set only when `vendor_boot` is true
 	// and `header_version` is greater than or equal to 4.
@@ -152,7 +152,7 @@
 	dtb := android.PathForModuleSrc(ctx, dtbName)
 	cmd.FlagWithInput("--dtb ", dtb)
 
-	cmdline := proptools.String(b.properties.Cmdline)
+	cmdline := strings.Join(b.properties.Cmdline, " ")
 	if cmdline != "" {
 		flag := "--cmdline "
 		if vendor {