Comment 3 for bug 737846

Review of these patches:

hurd-pthread - all code is conditional on HURD, __GNU__, GC_GNU_THREADS defines. I believe this is safe to enable cross-architecture.
alpha-ieee, alpha-ieee-doc - patching arch-specific code / documentation, safe to enable cross-architecture.
mudflap-nocheck - alpha-specific workaround, not appropriate to enable everywhere. Should maybe be dropped? (dates back to 2009-03 or earlier, no idea if anyone's tested without on alpha lately or if anyone even cares now)
libjava-armel-unwind - arm-specific workaround for a bug somewhere else (possibly in libjava/classpath/native/jni/gtk-peer/gnu_java_awt_peer_gtk_GtkToolkit.c, according to the referenced thread). Should not be applied cross-platform, maybe should be dropped instead (after checking that the underlying bug is fixed)
powerpc_remove_many - conditional on __SPE__, I believe this is safe.
ibm-branch - big scary patch touching common files, not safe to include on !powerpc64 :(
kbsd-gnu.diff - clean conditions, could be applied to all archs
hurd-changes.diff - touches hurd-specific code, safe to enable
libstdc++-no-testsuite - disabling testsuite, should not be enabled cross-architecture, don't know if it's still needed but it was added fairly recently (maverick)
libmudflap-no-testsuite - idem
gcc-ppc64-O3 - looks arch-specific

So there is some room for improvement in terms of patches being arch-specific when they shouldn't need to be, but not enough to get us all the way there for multiarch. I think the better solution is simply to push the debian_patches list to an arch-specific file, and put a footer at the bottom of README.Debian.gz that explains where to look.