[MachO] Pad section data to pointer size bytes

https://reviews.llvm.org/D74273

Pad macho section data to pointer size bytes, so that relocation
table and symbol table following section data will be pointer size
aligned.

Patch by pguo.

lib/MC/MachObjectWriter.cpp

@@ -831,11 +831,11 @@ uint64_t MachObjectWriter::writeObject(MCAssembler &Asm,
     SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
   }
 
-  // The section data is padded to 4 bytes.
+  // The section data is padded to pointer size bytes.
   //
   // FIXME: Is this machine dependent?
   unsigned SectionDataPadding =
-      offsetToAlignment(SectionDataFileSize, Align(4));
+      offsetToAlignment(SectionDataFileSize, is64Bit() ? Align(8) : Align(4));
   SectionDataFileSize += SectionDataPadding;
 
   // Write the prolog, starting with the header and load command...

test/MC/MachO/darwin-x86_64-diff-relocs.s

@@ -147,7 +147,7 @@ L3:
 // CHECK:     Size: 0x5E
 // CHECK:     Offset: 384
 // CHECK:     Alignment: 0
-// CHECK:     RelocationOffset: 0x26C
+// CHECK:     RelocationOffset: 0x270
 // CHECK:     RelocationCount: 12
 // CHECK:     Type: Regular (0x0)
 // CHECK:     Attributes [ (0x800004)
@@ -174,7 +174,7 @@ L3:
 // CHECK:     Size: 0x8E
 // CHECK:     Offset: 478
 // CHECK:     Alignment: 0
-// CHECK:     RelocationOffset: 0x2CC
+// CHECK:     RelocationOffset: 0x2D0
 // CHECK:     RelocationCount: 16
 // CHECK:     Type: Regular (0x0)
 // CHECK:     Attributes [ (0x4)

test/MC/MachO/variable-exprs.s

@@ -298,7 +298,7 @@ Lt0_x = Lt0_a - Lt0_b
 // CHECK-X86_64:     Size: 0x38
 // CHECK-X86_64:     Offset: 385
 // CHECK-X86_64:     Alignment: 0
-// CHECK-X86_64:     RelocationOffset: 0x1BC
+// CHECK-X86_64:     RelocationOffset: 0x1C0
 // CHECK-X86_64:     RelocationCount: 9
 // CHECK-X86_64:     Type: Regular (0x0)
 // CHECK-X86_64:     Attributes [ (0x0)