Another FWIW, building on i386 with -O1 instead of -O2 and dropping -fno-strict-aliasing is successful.
Where can one find the differences between -O1 and -O2 in GCC 7?
What changed between GCC 6 and 7 would be useful too.
--- a/debian/rules
+++ b/debian/rules
@@ -7,7 +7,10 @@
include /usr/share/dpkg/default.mk
-export DEB_CFLAGS_MAINT_APPEND = -fno-strict-aliasing
+ifneq (,$(filter $(DEB_HOST_ARCH),i386))
+ export DEB_CFLAGS_MAINT_STRIP=-O2
+ export DEB_CFLAGS_MAINT_APPEND=-O1
+endif
%:
dh $@
