autotools: Set a default buildDir

So that the un-changed optimization in setBuildDirectory works
correctly.

Change-Id: Ie31fb2722c663cd0f998458d536181f47c83a37d
Reviewed-by: Daniel Teske <daniel.teske@theqtcompany.com>

src/plugins/autotoolsprojectmanager/autotoolsbuildconfiguration.cpp

@@ -64,7 +64,11 @@ using namespace ProjectExplorer::Constants;
 //////////////////////////////////////
 AutotoolsBuildConfiguration::AutotoolsBuildConfiguration(Target *parent)
     : BuildConfiguration(parent, Core::Id(AUTOTOOLS_BC_ID))
-{ }
+{
+  // /<foobar> is used so the un-changed check in setBuildDirectory() works correctly.
+  // The leading / is to avoid the relative the path expansion in BuildConfiguration::buildDirectory.
+  BuildConfiguration::setBuildDirectory(Utils::FileName::fromString(QString::fromLatin1("/<foobar>")));
+}
 
 NamedWidget *AutotoolsBuildConfiguration::createConfigWidget()
 {