[llvm-objcopy][MachO] Fix build

Some compilers are confused when the same name is used in different contexts.
Rename the field Section to unbreak the build.
(Caught by the buildbot http://lab.llvm.org:8011/builders/clang-with-thin-lto-ubuntu/builds/22374)
diff --git a/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp b/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp
index b12e39c..cf32f00 100644
--- a/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp
+++ b/llvm/tools/llvm-objcopy/MachO/MachOReader.cpp
@@ -222,7 +222,7 @@
             // if we encounter an invalid relocation.
             assert(SymbolNum >= 1 && SymbolNum <= Sections.size() &&
                    "Invalid section index.");
-            Reloc.Section = Sections[SymbolNum - 1];
+            Reloc.Sec = Sections[SymbolNum - 1];
           }
         }
 }
diff --git a/llvm/tools/llvm-objcopy/MachO/MachOWriter.cpp b/llvm/tools/llvm-objcopy/MachO/MachOWriter.cpp
index 4a8d1ae..1cb67d0 100644
--- a/llvm/tools/llvm-objcopy/MachO/MachOWriter.cpp
+++ b/llvm/tools/llvm-objcopy/MachO/MachOWriter.cpp
@@ -243,7 +243,7 @@
         if (!RelocInfo.Scattered) {
           const uint32_t SymbolNum = RelocInfo.Extern
                                          ? (*RelocInfo.Symbol)->Index
-                                         : (*RelocInfo.Section)->Index;
+                                         : (*RelocInfo.Sec)->Index;
           RelocInfo.setPlainRelocationSymbolNum(SymbolNum, IsLittleEndian);
         }
         if (IsLittleEndian != sys::IsLittleEndianHost)
diff --git a/llvm/tools/llvm-objcopy/MachO/Object.h b/llvm/tools/llvm-objcopy/MachO/Object.h
index 703c31f..a2c0074 100644
--- a/llvm/tools/llvm-objcopy/MachO/Object.h
+++ b/llvm/tools/llvm-objcopy/MachO/Object.h
@@ -165,7 +165,7 @@
   // The referenced symbol entry. Set if !Scattered && Extern.
   Optional<const SymbolEntry *> Symbol;
   // The referenced section. Set if !Scattered && !Extern.
-  Optional<const Section *> Section;
+  Optional<const Section *> Sec;
   // True if Info is a scattered_relocation_info.
   bool Scattered;
   // True if the r_symbolnum points to a section number (i.e. r_extern=0).