Fix linux-sgx build error when libc-wasi is disabled (#2997)

Compilation error was reported when `cmake -DWAMR_BUILD_LIBC_WASI=0`
on linux-sgx platform:
```
core/shared/platform/linux-sgx/sgx_socket.c:8:10:
fatal error: libc_errno.h: No such file or directory
    8 | #include "libc_errno.h"
      |          ^~~~~~~~~~~~~~
```
After fixing, both `cmake -DWAMR_BUILD_LIBC_WASI=1` and
`WAMR_BUILD_LIBC_WASI=0` work good.

core/shared/platform/linux-sgx/sgx_platform.c

@@ -119,6 +119,18 @@ strcpy(char *dest, const char *src)
     return dest;
 }
 
+#if WASM_ENABLE_LIBC_WASI == 0
+bool
+os_is_handle_valid(os_file_handle *handle)
+{
+    assert(handle != NULL);
+
+    return *handle > -1;
+}
+#else
+/* implemented in posix_file.c */
+#endif
+
 void *
 os_mmap(void *hint, size_t size, int prot, int flags, os_file_handle file)
 {

core/shared/platform/linux-sgx/sgx_socket.c

@@ -5,10 +5,11 @@
 
 #include "platform_api_vmcore.h"
 #include "platform_api_extension.h"
-#include "libc_errno.h"
 
 #ifndef SGX_DISABLE_WASI
 
+#include "libc_errno.h"
+
 #define TRACE_OCALL_FAIL() os_printf("ocall %s failed!\n", __FUNCTION__)
 
 /** OCALLs prototypes **/