Move build_config.h from chromium/base/build to chromium/base

Moved build_config.h to mimic the include path on ChromeOS and Brillo.
On those platform, this file is included as just "build/build_config.h"

Change-Id: Ia8a30299cc7f485b38eeeddef2e5210644b3d2a3
Reviewed-on: https://weave-review.googlesource.com/1811
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
diff --git a/third_party/modp_b64/modp_b64.cc b/third_party/modp_b64/modp_b64.cc
index 8db2ed1..6624ec5 100644
--- a/third_party/modp_b64/modp_b64.cc
+++ b/third_party/modp_b64/modp_b64.cc
@@ -45,7 +45,7 @@
 /* public header */
 #include "modp_b64.h"
 
-#include <base/build/build_config.h>
+#include <build/build_config.h>
 
 #undef WORDS_BIGENDIAN
 #if !defined(ARCH_CPU_LITTLE_ENDIAN)