There are a few changes in glibc-2.10 that might make your software fail to build with it, please refer to my blog post  if you're not sure what the problem is.
And no I don't usually provide emerge --info with these bugs because they are caused by glibc-2.10!
Created attachment 193514 [details]
# Samuli Suominen <email@example.com> (19 Jul 2009)
# Doesn't compile wrt #272602. ALSA support broken wrt #98769.
# No upstream. Masked for removal.
Created attachment 198634 [details, diff]
Fix compilation with glibc-2.10.1 and also remove some warnings
It would be a pity to see this nice package die just because a few lines
need to be patched. The attached patch is a bit longer since it also fixes
the "obsolete conversion" warnings.
I do not know what should be wrong w.r.t. autotools - here it compiles fine
and shows no strange warnings.
Moreover, although alsa output from bug 98769 would be nice, it works fine
with oss (also with oss emulation of alsa): Also many other packages have
problems with alsa (e.g. mplayer is on my system unusable with alsa).
Try to eautoreconf it for example; it's a prereq to get the ALSA bug fixed... since it modifies configure.in, IIRC.
+ 22 Jul 2009; Samuli Suominen <firstname.lastname@example.org> sidplay-2.0.9.ebuild,
+ Fix building with glibc-2.10+ wrt #272602, thanks to Martin Väth and
+ Diego E. Pettenò.
ALSA support fixing left.