silence boost Unknown compiler version message with VS2012

Change-Id: I8f81cc7491da81c33bd27d084a8e7b19e5c637a7
Reviewed-on: https://gerrit.libreoffice.org/784Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>

boost/boost.vc2012.patch

@@ -12,3 +12,14 @@
  
  #if (_MSC_VER <= 1600)
  // MSVC (including the latest checked version) has not yet completely 
+@@ -269,8 +269,8 @@
+ #error "Compiler not supported or configured - please reconfigure"
+ #endif
+ //
+-// last known and checked version is 1600 (VC10, aka 2010):
+-#if (_MSC_VER > 1600)
++// last known and checked version is 1700 (VC12, aka 2012):
++#if (_MSC_VER > 1700)
+ #  if defined(BOOST_ASSERT_CONFIG)
+ #     error "Unknown compiler version - please run the configure tests and report the results"
+ #  else