unrar: Add global.cpp back to BUILD file

global.cpp was removed in crrev.com/c/984113 because it uses
`pragma hdrstop`. This CL removes that directive when building Chromium.

Bug: 750327
Change-Id: I8d6af052bc6c9a9c10a6b824fd499b548c7714a6
Reviewed-on: https://chromium-review.googlesource.com/1037917Reviewed-by: Nathan Parker <nparker@chromium.org>
Commit-Queue: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555435}

third_party/unrar/BUILD.gn

@@ -24,6 +24,7 @@ if (safe_browsing_mode == 1) {
       "src/filestr.cpp",
       "src/find.cpp",
       "src/getbits.cpp",
+      "src/global.cpp",
       "src/hash.cpp",
       "src/headers.cpp",
       "src/isnt.cpp",

third_party/unrar/src/global.cpp

 #define INCLUDEGLOBAL
 
+#if !defined(CHROMIUM_UNRAR)
 #if defined(__BORLANDC__) || defined(_MSC_VER)
 #pragma hdrstop
 #endif
+#endif  // defined(CHROMIUM_UNRAR)
 
 #include "rar.hpp"