BaseTools: Treat GenFds.py as a python module

Since GenFds.py import modules from its own directory, add "-m" to the
python parameters so that they can import its own modules after adopting
absolute import.

Contributed-under: TianoCore Contribution Agreement 1.1
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>

BaseTools/BinWrappers/PosixLike/GenFds

@@ -11,4 +11,4 @@ dir=$(dirname "$full_cmd")
 cmd=${full_cmd##*/}
 
 export PYTHONPATH="$dir/../../Source/Python${PYTHONPATH:+:"$PYTHONPATH"}"
-exec "${python_exe:-python}" "$dir/../../Source/Python/$cmd/$cmd.py" "$@"
+exec "${python_exe:-python}" -m $cmd.$cmd "$@"