Data race in the goflag global variable in the rcutorture test.
Description of problem:
A data race involving the `goflag` global variable in `tests/unit/rcutorture.c` was identified using TSAN.
Steps to reproduce:
```sh
QEMU_BUILD_DIR=<path to the QEMU build directory>
QEMU_DIR=<path to the QEMU repository directory>
configure --enable-tsan --cc=clang --cxx=clang++ --enable-trace-backends=ust --enable-fdt=system --disable-slirp
make tests/unit/rcutorture
MALLOC_PERTURB_=194 G_TEST_BUILDDIR=$QEMU_BUILD_DIR/tests/unit G_TEST_SRCDIR=$QEMU_DIR/tests/unit $QEMU_BUILD_DIR/tests/unit/rcutorture --tap -k
```