esp32: enable LIBC_ARCH_ATOMIC

[yamt]

Summary

fixes a build issue in apache/nuttx-apps#1723

Impact

Testing

build tested

[gustavonihei]

@yamt Could you please explain about the need for this patch?

ESP32's toolchain does implement the atomic builtins from GCC, so as long as the atomic operation does not include big numbers, this patch shouldn't be necessary.
Furthermore, this patch will impose performance overhead due to the use of OS-assisted locking via critical sections instead of the conditional load/store instructions from the Xtensa ISA.