[lldb] Flip the conservative answer for StackID::IsCFAOnStack

The optimization in swiftlang#7877
accidentally changed the default answer for this function.

It's important to default to "On Stack" when we don't know, because that's where
most CFAs live, and because we don't want to trigger the expensive heap
comparisons unless we're absolutely sure the CFA is on the heap.

(cherry picked from commit 57757e9)

Author: felipepiovezan

lldb/source/Target/StackID.cpp

@@ -19,12 +19,13 @@ using namespace lldb_private;
 
 bool StackID::IsCFAOnStack(Process &process) const {
   if (m_cfa_on_stack == eLazyBoolCalculate) {
-    m_cfa_on_stack = eLazyBoolNo;
+    // Conservatively assume stack memory
+    m_cfa_on_stack = eLazyBoolYes;
     if (m_cfa != LLDB_INVALID_ADDRESS) {
       MemoryRegionInfo mem_info;
       if (process.GetMemoryRegionInfo(m_cfa, mem_info).Success())
-        if (mem_info.IsStackMemory() == MemoryRegionInfo::eYes)
-          m_cfa_on_stack = eLazyBoolYes;
+        if (mem_info.IsStackMemory() == MemoryRegionInfo::eNo)
+          m_cfa_on_stack = eLazyBoolNo;
     }
   }
   return m_cfa_on_stack == eLazyBoolYes;