[mach-o] Add support and test cases for parsing tentative definitions

llvm-svn: 208919
diff --git a/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp b/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
index 1ffb429..1012319 100644
--- a/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
+++ b/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
@@ -726,6 +726,8 @@
 void MachOFileLayout::writeSectionContent() {
   for (const Section &s : _file.sections) {
     // Copy all section content to output buffer.
+    if (s.type == llvm::MachO::S_ZEROFILL)
+      continue;
     uint32_t offset = _sectInfo[&s].fileOffset;
     uint8_t *p = &_buffer[offset];
     memcpy(p, &s.content[0], s.content.size());