liblog: make liblog_headers truly stand-alone.

We don't want to imply dependencies on libc or libc++.

Bug: https://issuetracker.google.com/issues/119713191
Test: boots
Change-Id: I4abe312e73fad3ca8e96abd328b16387507baed4

liblog/Android.bp

@@ -46,6 +46,8 @@ cc_library_headers {
     vendor_available: true,
     recovery_available: true,
     export_include_dirs: ["include"],
+    system_shared_libs: [],
+    stl: "none",
     target: {
         windows: {
             enabled: true,