[v3] tweak -ffunction-sections configure test

[David Edelsohn]

>>>>> Benjamin Kosnik writes:

> This adds -g to the compile line when testing -ffunction-sections, in 
> the hopes that the results will be more accurate on AIX and cygwin, and 
> reflect actual usage.

Ben,

	If you are going to change the behavior of libstdc++ on AIX, it
would be considerate for you to ask me or at least alert me.  The subject
line is not something that would attract my attention.

	This patch broke -ffunction-sections support in libstdc++ on AIX.
This is a regression.  "-g" causes G++ to emit a warning that
"-ffunction-sections may affect debugging" and "-Werror" causes the
warning becomes an error.  This means that the -ffunction-sections
configure test now fails, disabling that option when building libstdc++.
The option should not be disabled -- it is a performance optimization on
AIX that functions correctly.

	This now is PR libstdc++/35597.  Please revert the -g change.

Thanks, David