fix(relinker): keep test artifacts in the build tree

The tests build their working directories with tempfile.TemporaryDirectory()
and std::filesystem::temp_directory_path(), so every executable they generate
lands in the user's system temp directory. On Windows, Microsoft Defender
quarantines those generated binaries as Trojan:Win32/Wacatac.H!ml, and the
nine tests that run one fail with WinError 5 (access denied) on a clean
checkout: autorun_exit_status, optional_plt, empty_tls, tls_function_coverage,
executable_segments, windows_icon, guest_needed_modules,
guest_module_directories and windows_import_modules.

Point TMPDIR, TEMP and TMP at a build-local directory for every test
registered here, so generated executables stay inside the build tree. Test
artifacts are then removed with the build directory, and a contributor who
needs an antivirus exclusion can scope it to the build tree instead of the
system temp directory.

core/relinker/CMakeLists.txt

@@ -735,6 +735,12 @@ if(BUILD_TESTING)
         )
         add_test(NAME reloc_table_bounds COMMAND reloc_table_bounds_tests $<TARGET_FILE:relinker>)
     endif()
+
+    set(relinkerTestTemp ${CMAKE_CURRENT_BINARY_DIR}/test-temp)
+    file(MAKE_DIRECTORY ${relinkerTestTemp})
+    get_property(relinkerTests DIRECTORY PROPERTY TESTS)
+    set_tests_properties(${relinkerTests} PROPERTIES ENVIRONMENT_MODIFICATION
+        "TMPDIR=set:${relinkerTestTemp};TEMP=set:${relinkerTestTemp};TMP=set:${relinkerTestTemp}")
 endif()
 
 if(BUILD_TESTING AND Python3_Interpreter_FOUND)