[Docs] Modernize references to macOS

This updates all places in documentation that refer to "Mac OS X", "OS X", etc.
to instead use the modern name "macOS" when no specific version number is

If a specific version is mentioned, this attempts to use the OS name at the time
of that version:

* Mac OS X for 10.0 - 10.7
* OS X for 10.8 - 10.11
* macOS for 10.12 - present

Reviewers: JDevlieghere

Subscribers: mgorny, christof, arphaman, cfe-commits, lldb-commits, libcxx-commits, llvm-commits

Tags: #clang, #lldb, #libc, #llvm

Differential Revision: https://reviews.llvm.org/D62654

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@362113 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/index.rst b/docs/index.rst
index 9e53b41..a4e21bb 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -50,7 +50,7 @@
 iOS          ARM                      Clang        SjLj
 Linux        ARM                      Clang, GCC   EHABI
 Linux        i386, x86_64, ARM64      Clang, GCC   DWARF CFI
-Mac OS X     i386, x86_64             Clang, GCC   DWARF CFI
+macOS        i386, x86_64             Clang, GCC   DWARF CFI
 NetBSD       x86_64                   Clang, GCC   DWARF CFI
 Windows      i386, x86_64, ARM, ARM64 Clang        DWARF CFI
 ============ ======================== ============ ========================