Fix MSVC MT/MD incompatibility in PYBIND11_BUILD_ABI

Author: isuruf

include/pybind11/detail/internals.h

@@ -311,11 +311,11 @@ struct type_info {
 #endif
 
 /// On Linux/OSX, changes in __GXX_ABI_VERSION__ indicate ABI incompatibility.
-/// On MSVC, changes in _MSC_VER may indicate ABI incompatibility (#2898).
+/// On MSVC, mixing /MT and /MD will result in crashes. See (#4779)
 #ifndef PYBIND11_BUILD_ABI
 #    if defined(__GXX_ABI_VERSION)
 #        define PYBIND11_BUILD_ABI "_cxxabi" PYBIND11_TOSTRING(__GXX_ABI_VERSION)
-#    elif defined(_MSC_VER)
+#    elif defined(_MSC_VER) && defined(_MT)
 #        define PYBIND11_BUILD_ABI "_mscver" PYBIND11_TOSTRING(_MSC_VER)
 #    else
 #        define PYBIND11_BUILD_ABI ""