Fixed llvm-objcopy to add correct symbol table for ELF with program headers.

[aorlov]

Summary

This fixes the following bugs:
https://bugs.llvm.org/show_bug.cgi?id=43935

[jhenderson]

LGTM, with nit.

llvm/test/tools/llvm-objcopy/ELF/add-symbol-no-symtab.test

109

The name ProgramHeaders (i.e. with that specific spelling) is specific to the YAML, but the actual issue is to do with program headers in general in the object.

llvm/test/tools/llvm-objcopy/ELF/add-symbol-no-symtab.test

FileHeader:
   Data:    ELFDATA2LSB
   Type:    ET_DYN
   Machine: EM_X86_64
 DynamicSymbols:
   - Name:    dummy
     Binding: STB_GLOBAL
 Symbols: []
 ...
+
+## Check the created .symtab is correct when there are program headers.
+# RUN: yaml2obj --docnum=4 %s -o %t4
+# RUN: llvm-objcopy %t4 %t4.add --add-symbol foo=1234
+# RUN: llvm-readelf -s %t4.add | FileCheck --check-prefix=SEC4 %s
+
+# SEC4:      0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   UND 
+# SEC4-NEXT: 1: 00000000000004d2     0 NOTYPE  GLOBAL DEFAULT   ABS foo
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_X86_64
+Sections:
+  - Name:    .foo
+    Type:    SHT_PROGBITS
+ProgramHeaders:
+  - Type:     PT_LOAD
+    FirstSec: .foo
+    LastSec:  .foo
+...

llvm/tools/llvm-objcopy/ELF/Object.cpp

 // Returns true IFF a section is wholly inside the range of a segment
 static bool sectionWithinSegment(const SectionBase &Sec, const Segment &Seg) {
   // If a section is empty it should be treated like it has a size of 1. This is
   // to clarify the case when an empty section lies on a boundary between two
   // segments and ensures that the section "belongs" to the second segment and
   // not the first.
   uint64_t SecSize = Sec.Size ? Sec.Size : 1;
 
+  // Ignore just added sections.
+  if (Sec.OriginalOffset == std::numeric_limits<uint64_t>::max())
+    return false;
+
   if (Sec.Type == SHT_NOBITS) {
     if (!(Sec.Flags & SHF_ALLOC))
       return false;
 
     bool SectionIsTLS = Sec.Flags & SHF_TLS;
     bool SegmentIsTLS = Seg.Type == PT_TLS;
     if (SectionIsTLS != SegmentIsTLS)
       return false;