FS-10690: [libblade, Build-System] Do not import BaseDir props if already imported.

w32/basedir.props

@@ -3,4 +3,7 @@
   <PropertyGroup Label="UserMacros" Condition=" '$(BaseDir)' == ''">
       <BaseDir>$(MSBuildThisFileDirectory)..\</BaseDir>
   </PropertyGroup>
+  <PropertyGroup>
+    <BaseDirImported>true</BaseDirImported>
+  </PropertyGroup>
 </Project>
\ No newline at end of file

w32/pcre-version.props

 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <ImportGroup Label="PropertySheets">
-    <Import Project="basedir.props"/>
+    <Import Project="basedir.props" Condition=" '$(BaseDirImported)' == ''"/>
   </ImportGroup>
   <PropertyGroup Label="UserMacros">
     <PCREVersion>8.34</PCREVersion>