[llvm-objcopy][ELF] Allow --dump-section to dump an empty non-SHT_NOBITS section

This is the ELF part of D75949.

GNU objcopy from binutils 2.35 onwards will support an empty non-SHT_NOBITS section as
well
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=e052e2ba295a65b6ea80cbc3f90495beca299c42

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D79339

test/tools/llvm-objcopy/ELF/dump-section.test

@@ -4,9 +4,11 @@
 # RUN: llvm-objcopy --dump-section .text=%t4 %t %t5
 # RUN: llvm-objcopy --dump-section .foo=%t6 %t %t7
 # RUN: not llvm-objcopy --dump-section .bar=%t8 %t %t9 2>&1 | FileCheck %s --check-prefix=NOBITS -DINPUT=%t
+# RUN: llvm-objcopy --dump-section .empty=%t.empty %t /dev/null
 # RUN: od -t x1 %t2 | FileCheck %s --ignore-case
 # RUN: od -t x1 %t6 | FileCheck %s --ignore-case --check-prefix=NON-ALLOC
 # RUN: wc -c %t2 | FileCheck %s --check-prefix=SIZE
+# RUN: wc -c %t.empty | FileCheck %s --check-prefix=EMPTY
 # RUN: diff %t2 %t3
 # RUN: diff %t4 %t3
 
@@ -26,6 +28,9 @@ Sections:
     Type:            SHT_PROGBITS
     Flags:           [ SHF_WRITE ]
     Content:         "CAFE"
+  - Name:            .empty
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
   - Name:            .bar
     Type:            SHT_NOBITS
     Flags:           [ SHF_WRITE ]
@@ -42,3 +47,5 @@ ProgramHeaders:
 # SIZE: 4
 
 # NOBITS: error: '[[INPUT]]': cannot dump section '.bar': it has no contents
+
+# EMPTY: 0

tools/llvm-objcopy/ELF/ELFObjcopy.cpp

@@ -288,7 +288,7 @@ static Error dumpSectionToFile(StringRef SecName, StringRef Filename,
                                Object &Obj) {
   for (auto &Sec : Obj.sections()) {
     if (Sec.Name == SecName) {
-      if (Sec.OriginalData.empty())
+      if (Sec.Type == SHT_NOBITS)
         return createStringError(object_error::parse_failed,
                                  "cannot dump section '%s': it has no contents",
                                  SecName.str().c_str());