Remove system.h.

The gyp files already define NOMINMAX and WIN32_LEAN_AND_MEAN.  windows.h
is also included via the D3D includes.

This ends up speeding up the build process significantly by not having
windows.h included in nearly every file.

Also fixes issues on non-windows systems by not having stdarg.h included
in debug.cpp.

Change-Id: Id32d9aac37a5a29df832a062dd8024302a798a1c
Reviewed-on: https://chromium-review.googlesource.com/183251
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/common/utilities.cpp b/src/common/utilities.cpp
index bd71058..b1e989b 100644
--- a/src/common/utilities.cpp
+++ b/src/common/utilities.cpp
@@ -9,6 +9,10 @@
 #include "common/utilities.h"
 #include "common/mathutil.h"
 
+#if defined(_WIN32)
+#include <windows.h>
+#endif
+
 #include <set>
 
 namespace gl
@@ -432,6 +436,7 @@
 
 std::string getTempPath()
 {
+#if defined (_WIN32)
     char path[MAX_PATH];
     DWORD pathLen = GetTempPathA(sizeof(path) / sizeof(path[0]), path);
     if (pathLen == 0)
@@ -448,6 +453,10 @@
     }
 
     return path;
+#else
+    UNIMPLEMENTED();
+    return "";
+#endif
 }
 
 void writeFile(const char* path, const void* content, size_t size)