Don’t set CMAKE_MSVC_RUNTIME_LIBRARY in debug builds (libjxl#3837)

Fixes libjxl#3834.

(cherry picked from commit 9f2402d)

CMakeLists.txt

@@ -225,7 +225,7 @@ if(JPEGXL_STATIC)
 
   # https://learn.microsoft.com/en-us/cpp/build/reference/md-mt-ld-use-run-time-library?view=msvc-170
   # https://cmake.org/cmake/help/latest/variable/CMAKE_MSVC_RUNTIME_LIBRARY.html
-  set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreaded)
+  set(CMAKE_MSVC_RUNTIME_LIBRARY "$<$<NOT:$<CONFIG:Debug>>:MultiThreaded>" CACHE STRING "")
 
   # Clang developers say that in case to use "static" we have to build stdlib
   # ourselves; for real use case we don't care about stdlib, as it is "granted",