ci: link os_compat for replay CMake tests; fix llvm-mingw mirrors

gcc -O0 keeps unused cst_test_util.h helpers that need os_*; clang GC'd
them so only the gcc CMake step failed. Prefer ghfast/ghproxy.net for the
llvm-mingw tarball (gitclone 500 / github unreachable on the runner).

CMakeLists.txt

@@ -237,7 +237,12 @@ foreach(t ${_CST_SMALL_TESTS})
   elseif(t STREQUAL test_json_baseline)
     add_executable(${t} tests/${t}.c src/json_baseline.c vendor/cjson/cJSON.c)
   elseif(t STREQUAL test_replay_starvation OR t STREQUAL test_replay_real)
-    add_executable(${t} tests/${t}.c src/ctl_parse.c src/json_baseline.c vendor/cjson/cJSON.c)
+    # cst_test_util.h static helpers reference os_*; gcc -O0 keeps unused ones
+    add_executable(${t} tests/${t}.c src/ctl_parse.c src/json_baseline.c
+      vendor/cjson/cJSON.c src/os_compat.c src/os_win.c)
+    if(WIN32)
+      target_link_libraries(${t} PRIVATE advapi32 user32)
+    endif()
   else()
     add_executable(${t} tests/test_mm_tool.c src/mm_tool.c)
   endif()