tools/gn: include exec_process.h in the source file.

exec_process.cc is the source file implementation of exec_process.h,
but somehow we forgot to include its corresponding header file. This
patch fixes that.

It also add it to the unittest file where it was also missing.

build_config.h was also included for the usage of OS_XXX macros.

BUG=None
R=mostynb@opera.com
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/1447513002

Cr-Commit-Position: refs/heads/master@{#359752}

tools/gn/exec_process.cc

@@ -2,12 +2,15 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "tools/gn/exec_process.h"
+
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/process/kill.h"
 #include "base/process/launch.h"
 #include "base/process/process.h"
+#include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include <windows.h>

tools/gn/exec_process_unittest.cc

@@ -2,11 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "tools/gn/exec_process.h"
+
 #include "base/command_line.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/strings/string_util.h"
+#include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
-#include "tools/gn/exec_process.h"
 
 #if defined(OS_WIN)
 #include "base/strings/utf_string_conversions.h"