test-server: fix to compile using mingw

Signed-off-by: Alejandro Mery <amery@geeks.cl>
mingw cmake and rebuild script [CI/DEV]

Signed-off-by: Alejandro Mery <amery@geeks.cl>
libev: remove all previous libev related code

except:
 * cmake integration (LWS_USE_LIBEV, LWS_WITH_LIBEV)
 * text in changelog and READMEs
 * server option (LWS_SERVER_OPTION_LIBEV)
 * code for printing the ev_backend() -- but kept disabled

Signed-off-by: Alejandro Mery <amery@geeks.cl>
context: move poll/win32 specifics into a sub-struct

Signed-off-by: Alejandro Mery <amery@geeks.cl>
context: introduce context->event_ops

Signed-off-by: Alejandro Mery <amery@geeks.cl>