[debugserver] Clear memory allocations after exec

After an exec, the inferior is a new process and none of these memory
regions are still allocated. Clear them out.

Differential Revision: https://reviews.llvm.org/D140253

(cherry picked from commit 58def62)

Author: bulbazord

lldb/tools/debugserver/source/MacOSX/MachProcess.mm

@@ -2285,6 +2285,7 @@ static bool mach_header_validity_test(uint32_t magic, uint32_t cputype) {
         m_thread_list.Clear();
         m_activities.Clear();
         m_breakpoints.DisableAll();
+        m_task.ClearAllocations();
       }
 
       if (m_sent_interrupt_signo != 0) {

lldb/tools/debugserver/source/MacOSX/MachTask.h

@@ -61,6 +61,7 @@ class MachTask {
 
   nub_addr_t AllocateMemory(nub_size_t size, uint32_t permissions);
   nub_bool_t DeallocateMemory(nub_addr_t addr);
+  void ClearAllocations();
 
   mach_port_t ExceptionPort() const;
   bool ExceptionPortIsValid() const;

lldb/tools/debugserver/source/MacOSX/MachTask.mm

@@ -999,6 +999,13 @@ static void get_threads_profile_data(DNBProfileDataScanType scanType,
   return false;
 }
 
+//----------------------------------------------------------------------
+// MachTask::ClearAllocations
+//----------------------------------------------------------------------
+void MachTask::ClearAllocations() {
+  m_allocations.clear();
+}
+
 void MachTask::TaskPortChanged(task_t task)
 {
   m_task = task;