fix: explicitly disable '-Wsuggest-attribute=format'

fix: explicitly disable '-Wsuggest-attribute=format'

Some older GCC version seems to enable '-Wsuggest-attribute=format' with
'-Wall' which results in unwanted warnings. Fixing this would require
modifications to the public headers which were done in the master
branch. As a fix for this stable branch, explicitly disable this warning
if the compiler supports it.

Change-Id: Ic71a9d0986c6f3d1eae561b15c8ffad54773e825
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>