Warning: Subdir-objects is disabled

[punit vara]

Today I was trying to bootstrap rtems. I have cloned repo.

git clone git://git.rtems.org/rtems.git

When I perform ./bootstrap It generates lots of warning

Makefile.am:24: warning: source file 'start/start.S' is in a subdirectory,
Makefile.am:24: but option 'subdir-objects' is disabled

I have found solution that I should add

AUTOMAKE_OPTIONS = subdir-objects

at top of Makefile.am But still I am getting warnings. What could be
the possible reason to stop this warnings. ? After that even I
modified configure.ac

AM_INIT_AUTOMAKE([subdir-objects])

Any suggestions please?