ADT/Triple: Helper to determine if we are targeting the Windows CRT

[majnemer]

Summary

This support will be utilized in things like clang to help check printf
format specifiers that are only valid when using the VSCRT.

[majnemer]

• Correct version of patch.

[chandlerc]

LGTM

include/llvm/ADT/Triple.h

bool isOSDarwin() const {
     return isMacOSX() || isiOS();
   }
 
   /// \brief Tests for either Cygwin or MinGW OS
   bool isOSCygMing() const {
     return getOS() == Triple::Cygwin || getOS() == Triple::MinGW32;
   }
 
+  /// \brief Is this a "Windows" OS targeting a "MSVCRT.dll" environment.
+  bool isOSMSVCRT() const {
+    return getOS() == Triple::Win32 || getOS() == Triple::MinGW32;
+  }
+
   /// isOSWindows - Is this a "Windows" OS.
   bool isOSWindows() const {
     return getOS() == Triple::Win32 || isOSCygMing();
   }
 
   /// \brief Tests whether the OS is NaCl (Native Client)
   bool isOSNaCl() const {
     return getOS() == Triple::NaCl;