Only implement tcontrol to handle reentrant triggers.

The spec says to only implement a single option. Option 2 gives software
more flexibility, and we already have an implementation. Let's use that
one. See also riscv-software-src#1777.

riscv/triggers.cc

@@ -112,6 +112,12 @@ bool trigger_t::textra_match(processor_t * const proc) const noexcept
 
 bool trigger_t::allow_action(const state_t * const state) const
 {
+  /* This implements option 1 from Section 5.4 in the Debug Spec.  Since we
+   * already implement option 2 (tcontrol), it's disabled for now.  Some day when
+   * there's a mechanism to tell spike which option to use, we can use this code
+   * again. */
+
+  /*
   if (get_action() == ACTION_DEBUG_EXCEPTION) {
     const bool mstatus_mie = state->mstatus->read() & MSTATUS_MIE;
     const bool sstatus_sie = state->sstatus->read() & MSTATUS_SIE;
@@ -122,6 +128,7 @@ bool trigger_t::allow_action(const state_t * const state) const
            (state->prv != PRV_S || state->v || !medeleg_breakpoint || sstatus_sie) &&
            (state->prv != PRV_S || !state->v || !medeleg_breakpoint || !hedeleg_breakpoint || vsstatus_sie);
   }
+  */
   return true;
 }