Tests: Improve FindPackageTest for in-source builds

Use a different directory name for the Exporter build tree so that it is
out-of-source even when the main test is in-source.

Tests/FindPackageTest/CMakeLists.txt

@@ -328,7 +328,7 @@ set(version "${version}.${v}")
 
 message(STATUS "Preparing export(PACKAGE) test project")
 try_compile(EXPORTER_COMPILED
-  ${FindPackageTest_BINARY_DIR}/Exporter
+  ${FindPackageTest_BINARY_DIR}/Exporter-build
   ${FindPackageTest_SOURCE_DIR}/Exporter
   CMakeTestExportPackage dummy
   CMAKE_FLAGS