Fix typo in previous commit to check for SSIZE_T on MSVC.

CMakeLists.txt

@@ -205,9 +205,9 @@ check_type_size(int64_t             SIZEOF_INT64_T)
 check_type_size(long                SIZEOF_LONG)
 check_type_size("long long"         SIZEOF_LONG_LONG)
 check_type_size("size_t"            SIZEOF_SIZE_T)
-if ("${CMAKE_C_COMPILER_ID}" STREQUAL "MSVC")
+if (MSVC)
 list(APPEND CMAKE_EXTRA_INCLUDE_FILES BaseTsd.h)
-check_type_size("SSIZE_T"           SIZEOF_SIZE_T)
+check_type_size("SSIZE_T"           SIZEOF_SSIZE_T)
 else()
 check_type_size("ssize_t"           SIZEOF_SSIZE_T)
 endif()