Update docs to reflect new minimum MSVC version requirement

Mailing list discussion about this:
http://lists.llvm.org/pipermail/llvm-dev/2016-September/104631.html

Code changes to simplify the ifdefs will come next, and can be reverted
without affecting the policy if someone needs it.

llvm-svn: 284660

Author: rnk

llvm/docs/CodingStandards.rst

@@ -127,17 +127,13 @@ unlikely to be supported by our host compilers.
 * Variadic templates: N2242_
 * Explicit conversion operators: N2437_
 * Defaulted and deleted functions: N2346_
-
-  * But not defaulted move constructors or move assignment operators, MSVC 2013
-    cannot synthesize them.
 * Initializer lists: N2627_
 * Delegating constructors: N1986_
 * Default member initializers (non-static data member initializers): N2756_
 
   * Only use these for scalar members that would otherwise be left
     uninitialized. Non-scalar members generally have appropriate default
-    constructors, and MSVC 2013 has problems when braced initializer lists are
-    involved.
+    constructors.
 
 .. _N2118: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2118.html
 .. _N2439: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2439.htm

llvm/docs/GettingStarted.rst

@@ -262,7 +262,7 @@ our build systems:
 
 * Clang 3.1
 * GCC 4.8
-* Visual Studio 2013
+* Visual Studio 2015
 
 Anything older than these toolchains *may* work, but will require forcing the
 build system with a special option and is not really a supported host platform.
@@ -296,8 +296,8 @@ Getting a Modern Host C++ Toolchain
 
 This section mostly applies to Linux and older BSDs. On Mac OS X, you should
 have a sufficiently modern Xcode, or you will likely need to upgrade until you
-do. On Windows, just use Visual Studio 2013 as the host compiler, it is
-explicitly supported and widely available. FreeBSD 10.0 and newer have a modern
+do. Windows does not have a "system compiler", so you must install either Visual
+Studio 2015 or a recent version of mingw64. FreeBSD 10.0 and newer have a modern
 Clang as the system compiler.
 
 However, some Linux distributions and some other or older BSDs sometimes have

llvm/docs/GettingStartedVS.rst

@@ -39,13 +39,13 @@ and software you will need.
 
 Hardware
 --------
-Any system that can adequately run Visual Studio 2013 is fine. The LLVM
+Any system that can adequately run Visual Studio 2015 is fine. The LLVM
 source tree and object files, libraries and executables will consume
 approximately 3GB.
 
 Software
 --------
-You will need Visual Studio 2013 or higher, with the latest Update installed. 
+You will need Visual Studio 2015 or higher, with the latest Update installed.
 
 You will also need the `CMake <http://www.cmake.org/>`_ build system since it
 generates the project files you will use to build with. CMake 2.8.12.2 is the