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/kernel_headers.go b/cc/kernel_headers.go
index fff419e..796de62 100644
--- a/cc/kernel_headers.go
+++ b/cc/kernel_headers.go
@@ -25,7 +25,7 @@
 func (stub *kernelHeadersDecorator) link(ctx ModuleContext, flags Flags, deps PathDeps, objs Objects) android.Path {
 	if ctx.Device() {
 		f := &stub.libraryDecorator.flagExporter
-		f.reexportSystemDirs(ctx.DeviceConfig().DeviceKernelHeaderDirs()...)
+		f.reexportSystemDirs(android.PathsForSource(ctx, ctx.DeviceConfig().DeviceKernelHeaderDirs())...)
 	}
 	return stub.libraryDecorator.linkStatic(ctx, flags, deps, objs)
 }