[llvm] Change llvm::sys::Mutex implementation to use STL-provided mutexes

[zturner]

Summary

Change llvm::sys::Mutex implementation to use std::mutex and std::recursive_mutex.

This patch deletes the platform specific mutex implementations, and delegates to the underlying STL implementation. Because STL mutex and recursive_mutex are implemented as separate classes, it is no longer possible to specify as a runtime param whether a recursive mutex is desired, and instead the decision must be made at compile time.

As part of this refactor, the ScopedLock class is deleted in favor of MutexGuard, which provides equivalent functionality.

To make reviewing easier, you can refer to the following table of equivalences in the format (old_type -> new_type)

SmartMutex<true>([true]) -> RecursiveDebugMutex

SmartMutex<false>([true]) -> RecursiveMutex
sys::Mutex -> SmartMutex<false>() -> RecursiveMutex

SmartMutex<true>(false) -> NonRecursiveDebugMutex
SmartMutex<false>(false) -> NonRecursiveMutex

[zturner]

Fix compiler errors on linux.

[zturner]

Going to resubmit this as a new patch, now that the issues are resolved.

lib/ExecutionEngine/OProfileJIT/OProfileWrapper.cpp

 #include <sys/stat.h>
 #include <unistd.h>
 
 #define DEBUG_TYPE "oprofile-wrapper"
 
 namespace {
 
 // Global mutex to ensure a single thread initializes oprofile agent.
-llvm::sys::Mutex OProfileInitializationMutex;
+llvm::sys::RecursiveMutex OProfileInitializationMutex;
 
 } // anonymous namespace
 
 namespace llvm {
 
 OProfileWrapper::OProfileWrapper()
 : Agent(0),
   OpenAgentFunc(0),

lib/Support/Unix/Process.inc

 extern "C" struct term *set_curterm(struct term *termp);
 extern "C" int del_curterm(struct term *termp);
 extern "C" int tigetnum(char *capname);
 #endif
 
 static bool terminalHasColors(int fd) {
 #ifdef HAVE_TERMINFO
   // First, acquire a global lock because these C routines are thread hostile.
-  static sys::Mutex M;
+  static sys::RecursiveMutex M;
   MutexGuard G(M);
 
   int errret = 0;
   if (setupterm((char *)nullptr, fd, &errret) != 0)
     // Regardless of why, if we can't get terminfo, we shouldn't try to print
     // colors.
     return false;
 

lib/Support/Unix/Signals.inc

 #if HAVE_MACH_MACH_H
 #include <mach/mach.h>
 #endif
 
 using namespace llvm;
 
 static RETSIGTYPE SignalHandler(int Sig);  // defined below.
 
-static SmartMutex<true> SignalsMutex;
+static llvm::sys::RecursiveDebugMutex SignalsMutex;
 
 /// InterruptFunction - The function to call if ctrl-c is pressed.
 static void (*InterruptFunction)() = nullptr;
 
 static std::vector<std::string> FilesToRemove;
 static std::vector<std::pair<void(*)(void*), void*> > CallBacksToRun;
 
 // IntSigs - Signals that represent requested termination. There's no bug