tesseract: fix build on macos

tesseract: fix build on macos

tesseract build script checks /proc/cpuinfo file, but this file is
not exist or darwin. This check is used for getting  optimized build
flags depends on CPU. This feature does not work in cross-compile
case and should be explicitly disabled.

This patch disables CPU detection using cmake option
BUILD_TRAINING_TOOLS=OFF.

Generated binaries (aarch64 target) are exactly the same on
Ubuntu 20.04 x86_64 and MacOS 11.6 arm64. Binaries generated on
Linux build host are not changed (the same checksums before and
after applying this patch).

Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>