The break 'depth' was used to indicate the number of if/else execution
enable mask's stack levels we need to discard when jumping from a break
statement to its enclosing switch or loop. However, each switch and
loop resets this depth at the end, which isn't correct for nested loops
and/or switches (note that switches contain if/else statements, and
loops use the same 'enable' masks as if/else).

This can be fixed either by using a stack to keep track of the break
depths of nested switch/loop statements, or by simply not jumping
directly from the break statement to the end of it's enclosing switch
or loop. The latter fix was chosen for this change, which assumes that
that it's uncommon for all vector lanes to become disabled at the break
statement and skip many instructions. An important exception to this is
breaking out of an infinite or long-running loop, but this is handled
by checking the break enable mask as part of the loop condition.

Change-Id: I57d2e03941e855faefd997442931ff8619eca73f
Reviewed-on: https://swiftshader-review.googlesource.com/15968Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>