The non-blocking API is missing on non-x86 platforms. This is seen by error
return from mysql_init(MYSQL_OPT_NONBLOCK, 0), and from null-pointer
segfault on all subsequent non-blocking calls.
The problem is missing check for ucontext in the CMake files, and missing
code to propagate the check to the my_context.h source file. ucontext is
used as a fallback for platforms where no hand-crafted assembler version is
available, such as ARM. Without ucontext fallback, the non-blocking API
See attached patch for a fix to add the proper check. Patch tested against
latest git on ARM.