Port printf tests to littlecheck and teach the tester how to run it

This adds support for .check files inside the tests directory. .check
files are tests designed to be run with littlecheck.

Port printf test to littlecheck and remove the printf.in test.

cmake/Tests.cmake

@@ -26,6 +26,9 @@ IF(NOT FISH_IN_TREE_BUILD)
     ADD_DEPENDENCIES(fish_tests tests_dir)
 ENDIF()
 
+# Copy littlecheck.py
+CONFIGURE_FILE(build_tools/littlecheck.py littlecheck.py COPYONLY)
+
 # Create the 'test' target.
 # Set a policy so CMake stops complaining about the name 'test'.
 CMAKE_POLICY(PUSH)