Move cross-files to the data subdirectory

We will add more data soon.

diff --git a/cross-files/README.md b/data/cross-files/README.md
similarity index 100%
rename from cross-files/README.md
rename to data/cross-files/README.md

diff --git a/cross-files/android_arm64_api28.txt b/data/cross-files/android_arm64_api28.txt
similarity index 100%
rename from cross-files/android_arm64_api28.txt
rename to data/cross-files/android_arm64_api28.txt

diff --git a/cross-files/mingw_w64_x86-64.txt b/data/cross-files/mingw_w64_x86-64.txt
similarity index 100%
rename from cross-files/mingw_w64_x86-64.txt
rename to data/cross-files/mingw_w64_x86-64.txt