[Support] Fix some Wundef warnings

For the _WIN32 macro, it is the definedness that matters rather than
the value.  Most uses of the macro already rely on the definedness.
This commit fixes the few remaining uses that relied on the value.

Differential Revision: https://reviews.llvm.org/D51105

llvm-svn: 340520
diff --git a/llvm/lib/Support/LockFileManager.cpp b/llvm/lib/Support/LockFileManager.cpp
index 77baf7a..c166230 100644
--- a/llvm/lib/Support/LockFileManager.cpp
+++ b/llvm/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