make installers: give MSVC setup "x86_amd64" instead of "x64" by default

The "x86_amd64" mode seems to work more often, especially with
Visual Studio Express installations.

INSTALL.txt

@@ -55,9 +55,11 @@ directory.
 On Mac OS X, see the notes below on git submodules, and then `make'
 (or `make in-place') creates a build in the "racket" directory.
 
-On Windows with Microsoft Visual Studio (version 9.0/2008 up to
-version 12.0/2013), see the notes below on git submodules, and then
-`nmake win32-in-place' creates a build in the "racket" directory.
+On Windows with Microsoft Visual Studio (any version between 2008/9.0
+and 2013/12.0), see the notes below on git submodules, and then `nmake
+win32-in-place' creates a build in the "racket" directory.  For
+information on configuring your command-line environment for Visual
+Studio, see "racket/src/worksp/README".
 
 In all cases, an in-place build includes (via links) packages that are
 in the "pkgs" directory.

pkgs/distro-build-pkgs/distro-build-client/doc.txt

@@ -216,8 +216,8 @@ Site-configuration keywords (where <string*> means no spaces, etc.):
   #:bits <integer> --- 32 or 64, affects Visual Studio mode
 
   #:vc <string*> --- provided to "vcvarsall/bat" to select the Visual
-    Studio build mode; the default is "x86" or "x64", depending on
-    `#:bits'
+    Studio build mode; the default is "x86" or "x86_amd64", depending
+    on `#:bits'
 
   #:sign-identity <string> --- provides an identity to be passed to
     `codesign` for code signing on Mac OS X (for all executables in a

pkgs/distro-build-pkgs/distro-build-server/drive-clients.rkt

@@ -299,7 +299,7 @@
   (define vc (or (get-opt c '#:vc)
                  (if (= bits 32)
                      "x86"
-                     "x64")))
+                     "x86_amd64")))
   (define j (or (get-opt c '#:j) 1))
   (define (cmd . args) 
     (list "cmd" "/c" (shell-protect (apply ~a args) platform)))

racket/src/worksp/README

@@ -2,8 +2,8 @@ This directory contains
 
   - solution files and project files for building minimal Racket and
     related executables with Microsoft Visual Studio 2008
-    (a.k.a. version 9.0) and up, which work with the Express version
-    of Visual Studio;
+    (a.k.a. version 9.0) and up, including the Express versions of
+    Visual Studio;
 
   - mzconfig.h which is a manual version of information that is gathered
     automatically when using the "configure" script;
@@ -43,14 +43,23 @@ As always, please report bugs via one of the following:
 Building Racket and GRacket
 ---------------------------
 
-If you're using Visual Studio, and if `cl.exe' and either `devenv.exe'
-or `vcexpress.exe' is in your path, then you can just run
+If you're using Visual Studio, and if `cl.exe' and `msbuild.exe'
+is in your path, then you can just run
     racket\src\worksp\build.bat
 from its own directory to perform all steps up to "Versioning",
 including the MzCOM steps.
 
+If `cl.exe' and `msbuild.exe' are not already in your path --- along
+with many associated environment variables --- then you can run
+"msvcprep.bat" to configure your environment, assuming that Visual
+Studio is in one of its usual locations. The "msvcprep.bat" script
+simply tries to find Visual Studio and run its "vcvarsall.bat". You
+may need to provide an argument such as "x86" or "x86_amd64" to select
+the build mode.
+
 If your MSVC environment is configured for 64-bit builds (e.g., by
-running "vcvarsall.bat" with "x64), then a 64-bit build is created.
+running "msvcprep.bat" or Microsoft's "vcvarsall.bat", with
+"x86_amd64" or "amd64"), then a 64-bit build is created.
 
 The CGC variants of Racket, GRacket, and MzCOM can be built via
 Visual Studio projects.  The 3m variants are built by a Racket script
@@ -127,9 +136,10 @@ Building Racket3m and GRacket3m
 
 After RacketCGC and GRacketCGC are built, you can can build 3m binaries:
 
-  1. Ensure that the Visual Studio command-line tools are in your path.
-     You may need to run "vcvarsall.bat" from your Visual Studio
-     installation, so that PATH and other environment variables are set.
+  1. Ensure that the Visual Studio command-line tools are in your
+     path.  You may need to run "msvcprep.bat" here or "vcvarsall.bat"
+     from your Visual Studio installation, so that PATH and other
+     environment variables are set.
 
   2. Change directories to racket\src\worksp\gc2 and run
 

racket/src/worksp/msvcprep.bat

@@ -1,6 +1,6 @@
 
-REM Expects "x86" or "x64" as an argument.
-REM Find Visual Studio in one of the usual places.
+REM  Find Visual Studio [Express] in one of the usual places.
+REM  Expects something like "x86", "amd64", or "x86_amd64" as an argument.
 
 set VCMODE=%1