emulators/citra: don't run tests on some non-x86

qemu-user-static hangs on armv6 and crashes on aarch64.

$ make test
[0/1] cd /wrkdirs/usr/ports/emulators/citra/work/.build && /usr/local/bin/ctest --force-new-ctest-process
Test project /wrkdirs/usr/ports/emulators/citra/work/.build

Start 1: tests

FAILED: CMakeFiles/test.util
cd /wrkdirs/usr/ports/emulators/citra/work/.build && /usr/local/bin/ctest --force-new-ctest-process
ninja: build stopped: subcommand failed.

• Error code 1

$ /wrkdirs/usr/ports/emulators/citra/work/.build/src/tests/tests

All tests passed (244 assertions in 14 test cases)