[build] Clean up no_rtti config handling

Don't assume that configs are always in the default list.

Bug: fuchsia:60253
Change-Id: Ic3bc5a94c31b167bf12d0552af10712ad45052cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/deps/icu/+/2424825
Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
1 file changed