[obj2yaml] - Zero initialize program headers. NFCI.

It allows to simplify the current code and also
might help for the code around.

It is also consistent with what we do for another headers,
e.g. section headers, elf file header etc.

Differential revision: https://reviews.llvm.org/D78627

llvm/lib/ObjectYAML/ELFEmitter.cpp

@@ -318,6 +318,7 @@ template <class ELFT>
 void ELFState<ELFT>::initProgramHeaders(std::vector<Elf_Phdr> &PHeaders) {
   for (const auto &YamlPhdr : Doc.ProgramHeaders) {
     Elf_Phdr Phdr;
+    zero(Phdr);
     Phdr.p_type = YamlPhdr.Type;
     Phdr.p_flags = YamlPhdr.Flags;
     Phdr.p_vaddr = YamlPhdr.VAddr;
@@ -759,16 +760,16 @@ void ELFState<ELFT>::setProgramHeaderLayout(std::vector<Elf_Phdr> &PHeaders,
       reportError("sections in the program header with index " +
                   Twine(PhdrIdx) + " are not sorted by their file offset");
 
-    uint64_t PhdrFileOffset = Fragments.empty() ? 0 : Fragments.front().Offset;
     if (YamlPhdr.Offset) {
-      if (!Fragments.empty() && *YamlPhdr.Offset > PhdrFileOffset)
+      if (!Fragments.empty() && *YamlPhdr.Offset > Fragments.front().Offset)
         reportError("'Offset' for segment with index " + Twine(PhdrIdx) +
                     " must be less than or equal to the minimum file offset of "
                     "all included sections (0x" +
-                    Twine::utohexstr(PhdrFileOffset) + ")");
-      PhdrFileOffset = *YamlPhdr.Offset;
+                    Twine::utohexstr(Fragments.front().Offset) + ")");
+      PHeader.p_offset = *YamlPhdr.Offset;
+    } else if (!Fragments.empty()) {
+      PHeader.p_offset = Fragments.front().Offset;
     }
-    PHeader.p_offset = PhdrFileOffset;
 
     // Find the maximum offset of the end of a section in order to set p_filesz
     // and p_memsz. When setting p_filesz, trailing SHT_NOBITS sections are not