[SystemZ][z/OS] Add missing include header to AutoConvert.cpp to fix …

…build (llvm#84909)

ba13fa2
added usages of `errnoAsErrorCode()` to AutoConvert.cpp, need to include
Error.h header to fix build failure.

llvm/lib/Support/AutoConvert.cpp

@@ -14,6 +14,7 @@
 #ifdef __MVS__
 
 #include "llvm/Support/AutoConvert.h"
+#include "llvm/Support/Error.h"
 #include <cassert>
 #include <fcntl.h>
 #include <sys/stat.h>