Index: lib/Support/COM.cpp
===================================================================
--- lib/Support/COM.cpp
+++ lib/Support/COM.cpp
@@ -18,6 +18,6 @@
 // Include the platform-specific parts of this class.
 #ifdef LLVM_ON_UNIX
 #include "Unix/COM.inc"
-#elif _WIN32
+#elif defined(_WIN32)
 #include "Windows/COM.inc"
 #endif
Index: lib/Support/CodeGenCoverage.cpp
===================================================================
--- lib/Support/CodeGenCoverage.cpp
+++ lib/Support/CodeGenCoverage.cpp
@@ -22,7 +22,7 @@
 
 #if LLVM_ON_UNIX
 #include <unistd.h>
-#elif _WIN32
+#elif defined(_WIN32)
 #include <windows.h>
 #endif
 
@@ -93,7 +93,7 @@
     std::string Pid =
 #if LLVM_ON_UNIX
         llvm::to_string(::getpid());
-#elif _WIN32
+#elif defined(_WIN32)
         llvm::to_string(::GetCurrentProcessId());
 #else
         "";
Index: lib/Support/Locale.cpp
===================================================================
--- lib/Support/Locale.cpp
+++ lib/Support/Locale.cpp
@@ -7,7 +7,7 @@
 namespace locale {
 
 int columnWidth(StringRef Text) {
-#if _WIN32
+#ifdef _WIN32
   return Text.size();
 #else
   return llvm::sys::unicode::columnWidthUTF8(Text);
@@ -15,7 +15,7 @@
 }
 
 bool isPrint(int UCS) {
-#if _WIN32
+#ifdef _WIN32
   // Restrict characters that we'll try to print to the lower part of ASCII
   // except for the control characters (0x20 - 0x7E). In general one can not
   // reliably output code points U+0080 and higher using narrow character C/C++
Index: lib/Support/LockFileManager.cpp
===================================================================
--- lib/Support/LockFileManager.cpp
+++ lib/Support/LockFileManager.cpp
@@ -24,7 +24,7 @@
 #include <sys/types.h>
 #include <system_error>
 #include <tuple>
-#if _WIN32
+#ifdef _WIN32
 #include <windows.h>
 #endif
 #if LLVM_ON_UNIX
@@ -295,7 +295,7 @@
   if (getState() != LFS_Shared)
     return Res_Success;
 
-#if _WIN32
+#ifdef _WIN32
   unsigned long Interval = 1;
 #else
   struct timespec Interval;
@@ -310,7 +310,7 @@
     // finish up and remove the lock file.
     // FIXME: Should we hook in to system APIs to get a notification when the
     // lock file is deleted?
-#if _WIN32
+#ifdef _WIN32
     Sleep(Interval);
 #else
     nanosleep(&Interval, nullptr);
@@ -329,7 +329,7 @@
       return Res_OwnerDied;
 
     // Exponentially increase the time we wait for the lock to be removed.
-#if _WIN32
+#ifdef _WIN32
     Interval *= 2;
 #else
     Interval.tv_sec *= 2;
@@ -340,7 +340,7 @@
     }
 #endif
   } while (
-#if _WIN32
+#ifdef _WIN32
            Interval < MaxSeconds * 1000
 #else
            Interval.tv_sec < (time_t)MaxSeconds