Make the call out to visual studio extremely resilient

windows_export.bat

@@ -1,16 +1,43 @@
-@echo on
+@echo off
+setlocal ENABLEDELAYEDEXPANSION
+
+if not "%1"=="x86" if not "%1"=="x64" (
+    echo Usage: windows_export.bat (x86 ^| x64^)
+    exit /b 1
+)
 
 :: This script invokes the Visual Studio linker to construct a static library file that can be used outside of Mingw.
 :: The unicorn.def file that it references below is produced by the Mingw compiler via a linker flag.
 :: The arch (x86 or x64) we are working on should be passed via the first argument to this script.
 
 :: Look up the Visual Studio install path via the registry
 :: http://stackoverflow.com/questions/445167/how-can-i-get-the-value-of-a-registry-key-from-within-a-batch-script
+:: There's no way to get the current installed VS version other than enumerating a version whitelist
 :: If anyone ever tells you that Windows is a reasonable operating system, they are wrong
-FOR /F "usebackq tokens=3*" %%A IN (`REG QUERY "HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\12.0" /v InstallDir`) DO (
-    set appdir=%%A %%B
+
+echo Searching for installed visual studio version...
+for %%V in (
+HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\12.0
+HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\14.0
+HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\15.0
+HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\12.0
+HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\14.0
+HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\15.0
+) do (
+    echo ...trying registry key %%V
+    for /F "usebackq tokens=3*" %%A IN (`REG QUERY %%V /v InstallDir 2^>NUL`) DO (
+        set appdir=%%A %%B
+    )
+    if not "!appdir!"=="" goto :break
+)
+:break
+
+if "%appdir%"=="" (
+    echo Could not find an installed visual studio version. Abandoning windows static lib export operation.
+) else (
+    :: Add the Visual Studio binaries to our path and run the linker
+    call "%appdir%..\..\VC\vcvarsall.bat" %1
+    call lib /machine:%1 /def:unicorn.def
 )
 
-:: Add the Visual Studio binaries to our path and run the linker
-call "%appdir%..\..\VC\vcvarsall.bat" %1
-call lib /machine:%1 /def:unicorn.def
+exit /b 0