msvc: Define main build/include directories in a single location

- Use a single file env.props for defining the main directories used when building.
  env.props resolves the base directory and defines overridable output directories,
  and is used by all other build files.
- Fix the build currently failing, basically because the preprocessing command for generating
  qstrdefs uses different include directories than the build itself does.
  (specifically, qstrdefs.h uses #include "py/mpconfig.h" since the fixes for #1022
  in 51dfcb4, so we need to use the base directory as include directory, not the py dir itself).
  So define a single variable containing the include directories instead and use it where needed.

windows/msvc/common.props

@@ -1,14 +1,17 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <ImportGroup Label="PropertySheets" />
+  <ImportGroup Label="PropertySheets">
+    <Import Project="env.props" />
+  </ImportGroup>
   <PropertyGroup Label="UserMacros" />
   <PropertyGroup>
-    <OutDir>$(ProjectDir)</OutDir>
-    <IntDir>$(ProjectDir)build\$(Configuration)$(Platform)\</IntDir>
+    <OutDir>$(PyOutDir)</OutDir>
+    <IntDir>$(PyBuildDir)$(Configuration)$(Platform)\</IntDir>
+    <PyIncDirs>$(PyBaseDir);$(PyBaseDir)windows;$(PyBaseDir)windows\msvc;$(PyBuildDir)</PyIncDirs>
   </PropertyGroup>
   <ItemDefinitionGroup>
     <ClCompile>
-      <AdditionalIncludeDirectories>.\;..\;.\build;.\msvc</AdditionalIncludeDirectories>
+      <AdditionalIncludeDirectories>$(PyIncDirs);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <PreprocessorDefinitions>_USE_MATH_DEFINES;_CRT_SECURE_NO_WARNINGS;_MBCS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <SDLCheck>false</SDLCheck>
       <WarningLevel>Level1</WarningLevel>

windows/msvc/env.props

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <PyBaseDir>$([System.IO.Path]::GetFullPath(`$(MSBuildThisFileDirectory)..\..`))\</PyBaseDir>
+    <PyBuildDir Condition="'$(PyBuildDir)'==''">$(MSBuildThisFileDirectory)build\</PyBuildDir>
+    <PyOutDir Condition="'$(PyOutDir)'==''">$(PyBaseDir)windows\</PyOutDir>
+    <PyEnvIncluded>True</PyEnvIncluded>
+  </PropertyGroup>
+</Project>

windows/msvc/genhdr.targets

@@ -1,12 +1,14 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" DefaultTargets="GenerateHeaders">
 
+  <Import Project="env.props" Condition="$(PyEnvIncluded)!=True"/>
+
   <Target Name="GenerateHeaders" DependsOnTargets="MakeQstrData;MakeVersionHeader">
   </Target>
 
   <PropertyGroup>
-    <SrcDir>$(MsBuildThisFileDirectory)..\..\py\</SrcDir>
-    <DestDir>$(MsBuildThisFileDirectory)..\build\genhdr\</DestDir>
+    <SrcDir>$(PyBaseDir)py\</SrcDir>
+    <DestDir>$(PyBuildDir)genhdr\</DestDir>
   </PropertyGroup>
 
   <Target Name="MakeDestDir">
@@ -17,10 +19,13 @@
   <Target Name="MakeQstrData" DependsOnTargets="MakeDestDir">
     <PropertyGroup>
       <PreProc>$(DestDir)qstrdefs.preprocessed.h</PreProc>
-      <QstrDefs>$(MsBuildThisFileDirectory)..\..\unix\qstrdefsport.h</QstrDefs>
+      <QstrDefs>$(PyBaseDir)unix\qstrdefsport.h</QstrDefs>
       <DestFile>$(DestDir)qstrdefs.generated.h</DestFile>
     </PropertyGroup>
-    <Exec Command="cl /nologo /I$(SrcDir) /I$(MsBuildThisFileDirectory).. /Fi$(PreProc) /P $(SrcDir)qstrdefs.h"/>
+    <ItemGroup>
+      <PyIncDirs Include="$(PyIncDirs)"/>
+    </ItemGroup>
+    <Exec Command="cl /nologo /I@(PyIncDirs, ' /I') /Fi$(PreProc) /P $(SrcDir)qstrdefs.h"/>
     <Exec Command="python $(SrcDir)makeqstrdata.py $(PreProc) $(QstrDefs) > $(DestFile).tmp"/>
     <Exec Command="fc /B $(DestFile).tmp $(DestFile) > NUL 2>&amp;1" IgnoreExitCode="true">
       <Output TaskParameter="ExitCode" PropertyName="FilesDiffer" />

windows/msvc/sources.props

@@ -1,8 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Build" ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <PropertyGroup>
-    <PyBaseDir>$(MsbuildThisFileDirectory)..\..\</PyBaseDir>
-  </PropertyGroup>
+  <Import Project="env.props" Condition="$(PyEnvIncluded)!=True"/>
   <ItemGroup>
     <ClCompile Include="$(PyBaseDir)py\*.c" />
     <ClCompile Include="$(PyBaseDir)extmod\*.c" />