* autogen.sh: Add option --makefile-name=gnulib.mk to gnulib-tool
* configure.ac: Add 'subdir-objects' to AM_INIT_AUTOMAKE,
add macro 'gl_GCC_VERSION_IFELSE' from coreutils project,
enable extra gcc warnings by default when running from Git repo,
disable several warnings for gnulib compilation
* lib/Makefile.am: New file
