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In current glibc, <sys/io.h> was removed along with support for outb/outw/outl :

commit 6b33f373c7b9199e00ba5fbafd94ac9bfb4337b1
Author: Florian Weimer <fweimer@redhat.com>
Date:   Wed May 29 16:53:09 2019 +0200

    arm: Remove ioperm/iopl/inb/inw/inl/outb/outw/outl support
    
    Linux only supports the required ISA sysctls on StrongARM devices,
    which are armv4 and no longer tested during glibc development
    and probably bit-rotted by this point.  (No reported test results,
    and the last discussion of armv4 support was in the glibc 2.19
    release notes.)

 ChangeLog                            |  10 ++++++
 NEWS                                 |   3 ++
 sysdeps/unix/sysv/linux/arm/Makefile |   2 +-
 sysdeps/unix/sysv/linux/arm/ioperm.c | 160 ++++++++++++++++++------------------------------------------------------------------------
 sysdeps/unix/sysv/linux/arm/sys/io.h |  47 ---------------------------
 5 files changed, 46 insertions(+), 176 deletions(-)

That causes the Xserver to fail to build on such platform as hw/xfree86/common/compiler.h both include <sys/io.h> and uses the glibc outb/outw/outl :

https://gitlab.freedesktop.org/xorg/xserver/blob/master/hw/xfree86/common/compiler.h#L761

Removing that entirely allows to build the Xserver (0001-compiler.h-Do-not-include-sys-io.h-on-ARM-with-glibc.patch) but we're obviously missing the outb/outw/outl that the drivers may use, so this would likely negatively impact the build of the Xorg drivers.