Change exportedDirs and exportedSystemDirs from []string to android.Paths

exportedDirs and exportedSystemDirs are now changed to android.Paths so
that we can later manipulate the paths via Rel(), etc.

Test: m

Change-Id: I6fb02ea4983bcebac351bc284f75b44885379e8f
diff --git a/cc/vndk_prebuilt.go b/cc/vndk_prebuilt.go
index 2cebb6d..a6d5085 100644
--- a/cc/vndk_prebuilt.go
+++ b/cc/vndk_prebuilt.go
@@ -143,7 +143,8 @@
 
 	if len(p.properties.Srcs) > 0 && p.shared() {
 		p.libraryDecorator.exportIncludes(ctx)
-		p.libraryDecorator.reexportSystemDirs(p.properties.Export_system_include_dirs...)
+		p.libraryDecorator.reexportSystemDirs(
+			android.PathsForModuleSrc(ctx, p.properties.Export_system_include_dirs)...)
 		p.libraryDecorator.reexportFlags(p.properties.Export_flags...)
 		// current VNDK prebuilts are only shared libs.
 		return p.singleSourcePath(ctx)