[clang-tidy] Fix 32bit platform MSVC

The previous fix only worked for 64bit MSVC, this one should fix all different
architectures.

llvm-svn: 316094

clang-tools-extra/test/clang-tidy/cppcoreguidelines-owning-memory-legacy-functions.cpp

@@ -10,7 +10,7 @@ using owner = T;
 } // namespace gsl
 
 extern "C" {
-using size_t = unsigned long long;
+using size_t = decltype(sizeof(void*));
 using FILE = int;
 
 void *malloc(size_t ByteCount);