I'm not sure yet if this is the gcc9 transition or any other.
But recently builds of qemu 4.0 broke in Eoan
An example build is at https://launchpad.net/ubuntu/+source/qemu/1:4.0+dfsg-0ubuntu2/+build/17252328
From the amd64 log:
9197 cc -iquote /<<BUILDDIR>>/qemu-4.0+dfsg/b/qemu/linux-user -iquote linux-user -iquote /<<BUILDDIR>>/qemu-4.0+dfsg/tcg -iquote /<<BUILDDIR>>/qemu-4.0+dfsg/tcg/i386 -I/<<BUILDDIR>>/qemu-4.0
9198 /<<BUILDDIR>>/qemu-4.0+dfsg/linux-user/ioctls.h:222:9: error: ‘SIOCGSTAMP’ undeclared here (not in a function); did you mean ‘SIOCSRARP’?
9199 222 | IOCTL(SIOCGSTAMP, IOC_R, MK_PTR(MK_STRUCT(STRUCT_timeval)))
9200 | ^~~~~~~~~~
9201 /<<BUILDDIR>>/qemu-4.0+dfsg/linux-user/syscall.c:4812:23: note: in definition of macro ‘IOCTL’
9202 4812 | { TARGET_ ## cmd, cmd, #cmd, access, 0, { __VA_ARGS__ } },
9203 | ^~~
9204 /<<BUILDDIR>>/qemu-4.0+dfsg/linux-user/ioctls.h:223:9: error: ‘SIOCGSTAMPNS’ undeclared here (not in a function); did you mean ‘SIOCGSTAMP_OLD’?
9205 223 | IOCTL(SIOCGSTAMPNS, IOC_R, MK_PTR(MK_STRUCT(STRUCT_timespec)))
9206 | ^~~~~~~~~~~~
9207 /<<BUILDDIR>>/qemu-4.0+dfsg/linux-user/syscall.c:4812:23: note: in definition of macro ‘IOCTL’
9208 4812 | { TARGET_ ## cmd, cmd, #cmd, access, 0, { __VA_ARGS__ } },
9209 | ^~~
9210 make[2]: *** [/<<BUILDDIR>>/qemu-4.0+dfsg/rules.mak:69: linux-user/syscall.o] Error 1
9211 make[2]: Leaving directory '/<<BUILDDIR>>/qemu-4.0+dfsg/b/qemu/aarch64-linux-user'
That build error is the same across all architectures.
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