Fix -Wshorten-64-to-32 warning on Android NDK when targeting x86

stat.h defines struct stat to use long long on Android NDK when
targeting x86; off_t however is defined as long, which is 32-bit (unlike
other Unix-like platforms). This results in a narrowing conversion which
produces a warning, and can also result in silently reading a prefix of
a huge file instead of a clean "out of memory" error.

There's no way for us to preserve the type exactly but always widening
to long long should be safe; get_file_size will proceed to check if
length actually fits into size_t which is what we ultimately need, and
that overflow check will fail on files that are >4 GB in size.

src/pugixml.cpp

@@ -4801,7 +4801,8 @@ PUGI_IMPL_NS_BEGIN
  // anything that's not a regular file doesn't have a coherent length
  if (!S_ISREG(st.st_mode)) return status_io_error;
 
- typedef off_t length_type;
+ // normally st_size is off_t, but Android NDK defines off_t as long (which is 32-bit when targeting x86 on Android) and st_size as long long
+ typedef long long length_type;
  length_type length = st.st_size;
  #elif defined(PUGI_IMPL_MSVC_CRT_VERSION) && PUGI_IMPL_MSVC_CRT_VERSION >= 1400
  // there are 64-bit versions of fseek/ftell, let's use them