C++20: don't use auto with u8"".

`u8""` has type `const char8_t*` rather than `const char*` in C++20, but
there's no `strlen()` for `char8_t*`, which breaks the build here.

Luckily this is the only place in the entire tree that does this. Let's
just remove the `auto`s.

Test: treehugger
Change-Id: I74c29889b4a60fdb642059c8699335c2abe99b34
1 file changed
tree: 4af5984d0e3569d455faf926d102b2d7b47b0fc1
  1. liblog/
  2. logcat/
  3. logd/
  4. logwrapper/
  5. rust/
  6. OWNERS
  7. PREUPLOAD.cfg
  8. TEST_MAPPING