sim/erc32: Rename EVENT_MAX -> MAX_EVENTS

EVENT_MAX is defined as 0x7FFFFFFF (INT_MAX) in winuser.h, so when
building on Windows, the value is overridden and compilation fails
because the array size of evbuf is too large.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28476


Approved-By: Tom Tromey <tom@tromey.com>