Automake version for 4.11.

[Chris Johns]

Hi,

I am seeing the following error bootstrapping on an updated MSYS2:

Unescaped left brace in regex is deprecated, passed through in regex; 
marked by <-- HERE in m/\${ <-- HERE ([^ \t=:+{}]+)}/ at 
/c/opt/rtems/4.11/bin/automake line 4033.

A quick search explains this as a new warning in perl v5.22 which MSYS2 
is shipping.

Should we clean this warning up by updating automake to 1.15 or leave it 
for 4.11 and come back to it for 4.11.1?

I think master should be updated.

Comments?

Chris