clang build error on i686

[Cole Robinson <crobinso@redhat.com>]

Hi, I'm hitting build errors with clang on i686 userspace on x86_64
kernel. Affects both qemu 6.0.0 and qemu.git, tested with fedora
clang-12.0.1~rc3-1.fc35.i686.

Full build log from the 6.0.0 build:
https://gist.githubusercontent.com/crobinso/7b1206044eac7326490b2adce829e861/raw/9dddef968051fd6383ba7adb9e595081ad4f8fa4/gistfile1.txt

Lots of errors like:

/usr/bin/ld: libqemu-aarch64-softmmu.fa.p/accel_tcg_cputlb.c.o: in
function `helper_atomic_cmpxchgq_le_mmu':
/builddir/build/BUILD/qemu-6.0.0/accel/tcg/atomic_template.h:86:
undefined reference to `__atomic_compare_exchange_8'
/usr/bin/ld: libqemu-aarch64-softmmu.fa.p/accel_tcg_cputlb.c.o: in
function `helper_atomic_xchgq_le_mmu':
/builddir/build/BUILD/qemu-6.0.0/accel/tcg/atomic_template.h:134:
undefined reference to `__atomic_exchange_8'

Also warnings like:

/builddir/build/BUILD/qemu-6.0.0/include/qemu/stats64.h:58:21: warning:
misaligned atomic operation may incur significant performance penalty;
the expected alignment (8 bytes) exceeds the actual alignment (4 bytes)
[-Watomic-alignment]
    uint64_t orig = qatomic_read__nocheck(&s->value);
                    ^
/builddir/build/BUILD/qemu-6.0.0/include/qemu/atomic.h:129:5: note:
expanded from macro 'qatomic_read__nocheck'
    __atomic_load_n(ptr, __ATOMIC_RELAXED)

Search the log for __atomic for other hits.

Thanks,
Cole