Use "_x64" instead of "amd64" for x64 MSW makefile builds.

Still accept "amd64" as a valid TARGET_CPU value but also accept, and
encourage people to use, "x64".

Add a new section about the build system changes to the change log and added a
mini-TOC to it to make navigating it a bit easier and show what changes are
there at a glance.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71978 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -10,6 +10,14 @@ INCOMPATIBLE CHANGES SINCE 2.8.x
         the "Changes Since wxWidgets 2.8" section of the manual,
         please read it if the explanation here is too cryptic.
 
+Table of contents of this section:
+
+ - Unicode-related changes
+ - wxODBC and contrib libraries removal
+ - Changes in behaviour not resulting in compilation errors
+ - Build system changes
+ - Major new features in this release
+
 
 Unicode-related changes
 -----------------------
@@ -470,6 +478,20 @@ Changes in behaviour visible to end users
   now the control scrolls if too much text is added.
 
 
+Build system changes
+--------------------
+
+- In wxMSW makefile builds, "_x64" is used instead of "_amd64" when compiling
+  for this architecture in the architecture-specific paths and library names.
+  TARGET_CPU can still be specified as "amd64" for compatibility but "x64"
+  should be used now.
+
+- Official wxMSW binaries, i.e. those built with OFFICIAL_BUILD=1, built with
+  MSVC now include the version of the compiler used and the architecture if
+  it's not the default "x86". E.g. a library built with MSVC 10 for amd64 is
+  called "wxbase294ud_vc110_amd64.dll" now.
+
+
 Major new features in this release
 ----------------------------------