[libomptarget][amdgpu][nfc] Replace use of gelf.h with libelf.h

[JonChesterfield]

Summary

AMDGPU can assume Elf64 so doesn't need to abstract over Elf32

Drop a few other unused headers at the same time. Now only llvm elf
and libelf are used by the plugin.

[jdoerfert]

LG

openmp/libomptarget/plugins/amdgpu/impl/system.cpp

 /*===--------------------------------------------------------------------------
  *              ATMI (Asynchronous Task and Memory Interface)
  *
  * This file is distributed under the MIT License. See LICENSE.txt for details.
  *===------------------------------------------------------------------------*/
-#include <gelf.h>
 #include <libelf.h>
 
 #include <cassert>
-#include <fstream>
-#include <iomanip>
-#include <set>
 #include <sstream>
 #include <string>
 
 #include "internal.h"
 #include "machine.h"
 #include "rt.h"
 
 #include "msgpack.h"
if (elf_kind(e) != ELF_K_ELF) {
     return failure;
   }
 
   size_t numpHdrs;
   if (elf_getphdrnum(e, &numpHdrs) != 0) {
     return failure;
   }
 
+  Elf64_Phdr *pHdrs = elf64_getphdr(e);
   for (size_t i = 0; i < numpHdrs; ++i) {
-    GElf_Phdr pHdr;
-    if (gelf_getphdr(e, i, &pHdr) != &pHdr) {
-      continue;
-    }
+    Elf64_Phdr pHdr = pHdrs[i];
+
     // Look for the runtime metadata note
     if (pHdr.p_type == PT_NOTE && pHdr.p_align >= sizeof(int)) {
       // Iterate over the notes in this segment
       address ptr = (address)binary + pHdr.p_offset;
       address segmentEnd = ptr + pHdr.p_filesz;
 
       while (ptr < segmentEnd) {
         Elf_Note *note = reinterpret_cast<Elf_Note *>(ptr);

openmp/libomptarget/plugins/amdgpu/src/rtl.cpp

 //
 //===----------------------------------------------------------------------===//
 
 #include <algorithm>
 #include <assert.h>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
-#include <elf.h>
-#include <fstream>
 #include <functional>
-#include <iostream>
 #include <libelf.h>
 #include <list>
 #include <memory>
 #include <mutex>
 #include <shared_mutex>
 #include <unordered_map>
 #include <vector>