Automatically disable fastmem and enable memcheck when there are any watchpoints.

- Move JitState::memcheck to JitOptions because it's an option.
- Add JitOptions::fastmem; switch JIT code to checking that rather than
  bFastmem directly.
- Add JitBase::UpdateMemoryOptions(), which sets both two JIT options
  (replacing the duplicate lines in Jit64 and JitIL that set memcheck
  from bMMU).
  - (!) The ARM JITs both had some lines that checked js.memcheck
    despite it being uninitialized in their cases.  I've added
    UpdateMemoryOptions to both.  There is a chance this could make
    something slower compared to the old behavior if the uninitialized
    value happened to be nonzero... hdkr should check this.
- UpdateMemoryOptions forces jo.fastmem and jo.memcheck off and on,
  respectively, if there are any watchpoints set.
- Also call that function from ClearCache.
- Have MemChecks call ClearCache when the {first,last} watchpoint is
  {added,removed}.

Enabling jo.memcheck (bah, confusing names) is currently pointless
because hitting a watchpoint does not interrupt the basic block.  That
will change in the next commit.

Source/Core/Common/BreakPoints.cpp

@@ -165,8 +165,13 @@ void MemChecks::AddFromStrings(const TMemChecksStr& mcstrs)
 
 void MemChecks::Add(const TMemCheck& _rMemoryCheck)
 {
+	bool had_any = HasAny();
 	if (GetMemCheck(_rMemoryCheck.StartAddress) == nullptr)
 		m_MemChecks.push_back(_rMemoryCheck);
+	// If this is the first one, clear the JIT cache so it can switch to
+	// watchpoint-compatible code.
+	if (!had_any)
+		jit->ClearCache();
 }
 
 void MemChecks::Remove(u32 _Address)
@@ -179,6 +184,8 @@ void MemChecks::Remove(u32 _Address)
 			return;
 		}
 	}
+	if (!HasAny())
+		jit->ClearCache();
 }
 
 TMemCheck *MemChecks::GetMemCheck(u32 address)