base/dockcross: Run docker with "-ti" only if a tty or pts is attached

This commit reverts f07ca00 (base: Do not add -i -t flags to run command
by default) and ensure tty is available before specifying the flags.

README.rst

@@ -211,7 +211,7 @@ Examples
 4. ``dockcross bash -c '$CC test/C/hello.c -o hello'``: Build the *hello.c* file
    with the compiler identified with the ``CC`` environmental variable in the
    build environment.
-5. ``dockcross --args -it bash``: Run an interactive shell in the build environment.
+5. ``dockcross bash``: Run an interactive shell in the build environment.
 
 Note that commands are executed verbatim. If any shell processing for
 environment variable expansion or redirection is required, please use

imagefiles/dockcross

@@ -179,7 +179,8 @@ fi
 #------------------------------------------------------------------------------
 # Now, finally, run the command in a container
 #
-docker run -t --rm \
+tty -s && TTY_ARGS=-ti || TTY_ARGS=
+docker run $TTY_ARGS --rm \
     -v $PWD:/work \
     $USER_IDS \
     $FINAL_ARGS \