[NFC][AIX][XCOFF] if the size of Csect is zero, the Csect do not need write any data into sections

[DiggerLin]

Summary

if the size of Csect is zero, the Csect do not need write any data into sections
for example, the TOC Csect has zero size, it do not need invoke a
Asm.writeSectionData(W.OS, Csect.MCCsect, Layout);

[daltenty]

LGTM

llvm/lib/MC/XCOFFObjectWriter.cpp

if (Section->Index == Section::UninitializedIndex || Section->IsVirtual)
       continue;
 
     assert(CurrentAddressLocation == Section->Address &&
            "We should have no padding between sections.");
     for (const auto *Group : Section->Groups) {
       for (const auto &Csect : *Group) {
         if (uint32_t PaddingSize = Csect.Address - CurrentAddressLocation)
           W.OS.write_zeros(PaddingSize);
+        if (Csect.Size)
           Asm.writeSectionData(W.OS, Csect.MCCsect, Layout);
         CurrentAddressLocation = Csect.Address + Csect.Size;
       }
     }
 
     // The size of the tail padding in a section is the end virtual address of
     // the current section minus the the end virtual address of the last csect
     // in that section.
     if (uint32_t PaddingSize =