Specify non global enums for bindgen update

The most recent bindgen update, 0.61.0, added the capability to support
global enumerations. Global enumerations are `const`s in the global
namespace instead of in an `impl` of the type. To maintain backwards
compatiblity and to scope enums consistently the non global version was
chosen.

non global

```rust
impl sgx_status_t {
    pub const SGX_SUCCESS: sgx_status_t = sgx_status_t(0);
}
```

global

```rust
pub const SGX_SUCCESS: sgx_status_t = sgx_status_t(0);
```

Author: nick-mobilecoin

core/build/src/lib.rs

@@ -63,7 +63,10 @@ pub fn sgx_builder() -> Builder {
     let builder = Builder::default()
         .derive_copy(false)
         .derive_debug(false)
-        .default_enum_style(EnumVariation::NewType { is_bitfield: false })
+        .default_enum_style(EnumVariation::NewType {
+            is_bitfield: false,
+            is_global: false,
+        })
         .prepend_enum_name(false)
         .use_core()
         .ctypes_prefix("core::ffi")

core/sys/types/build.rs

@@ -111,8 +111,7 @@ fn main() {
         ]);
     let mut builder = mc_sgx_core_build::sgx_builder()
         .header("wrapper.h")
-        .parse_callbacks(Box::new(callback))
-        .newtype_enum("_status_t");
+        .parse_callbacks(Box::new(callback));
 
     for t in CORE_TYPES.iter() {
         builder = builder.allowlist_type(t)