[Windows] Use TerminateProcess to exit without running destructors

If exiting using _Exit or ExitProcess, DLLs are still unloaded
cleanly before exiting, running destructors and other cleanup in those
DLLs. When the caller expects to exit without cleanup, running
destructors in some loaded DLLs (which can be either libLLVM.dll or
e.g. libc++.dll) can cause deadlocks occasionally.

This is an alternative to D102684.

Differential Revision: https://reviews.llvm.org/D102944

llvm/include/llvm/Support/Process.h

@@ -216,6 +216,10 @@ class Process {
   /// Use \arg NoCleanup for calling _exit() instead of exit().
   LLVM_ATTRIBUTE_NORETURN
   static void Exit(int RetCode, bool NoCleanup = false);
+
+private:
+  LLVM_ATTRIBUTE_NORETURN
+  static void ExitNoCleanup(int RetCode);
 };
 
 }

llvm/lib/Support/Process.cpp

@@ -98,7 +98,7 @@ void Process::Exit(int RetCode, bool NoCleanup) {
     CRC->HandleExit(RetCode);
 
   if (NoCleanup)
-    _Exit(RetCode);
+    ExitNoCleanup(RetCode);
   else
     ::exit(RetCode);
 }

llvm/lib/Support/Unix/Process.inc

@@ -460,3 +460,6 @@ unsigned llvm::sys::Process::GetRandomNumber() {
   return ::rand();
 #endif
 }
+
+LLVM_ATTRIBUTE_NORETURN
+void Process::ExitNoCleanup(int RetCode) { _Exit(RetCode); }

llvm/lib/Support/Windows/Process.inc

@@ -503,3 +503,9 @@ bool llvm::RunningWindows8OrGreater() {
   // Windows 8 is version 6.2, service pack 0.
   return GetWindowsOSVersion() >= llvm::VersionTuple(6, 2, 0, 0);
 }
+
+LLVM_ATTRIBUTE_NORETURN
+void Process::ExitNoCleanup(int RetCode) {
+  TerminateProcess(GetCurrentProcess(), RetCode);
+  llvm_unreachable("TerminateProcess doesn't return");
+}