[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/libcxx/trunk@362113 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/BuildingLibcxx.rst b/docs/BuildingLibcxx.rst
index c334269..06f8960 100644
--- a/docs/BuildingLibcxx.rst
+++ b/docs/BuildingLibcxx.rst
@@ -41,7 +41,7 @@
    .. warning::
      * Replacing your systems libc++ installation could render the system non-functional.
-     * Mac OS X will not boot without a valid copy of ``libc++.1.dylib`` in ``/usr/lib``.
+     * macOS will not boot without a valid copy of ``libc++.1.dylib`` in ``/usr/lib``.
 The instructions are for building libc++ on
diff --git a/docs/UsingLibcxx.rst b/docs/UsingLibcxx.rst
index e2af5c6..ef3023e 100644
--- a/docs/UsingLibcxx.rst
+++ b/docs/UsingLibcxx.rst
@@ -15,7 +15,7 @@
     $ clang++ -stdlib=libc++ test.cpp
     $ clang++ -std=c++11 -stdlib=libc++ test.cpp
-On OS X and FreeBSD libc++ is the default standard library
+On macOS and FreeBSD libc++ is the default standard library
 and the ``-stdlib=libc++`` is not required.
 .. _alternate libcxx:
@@ -34,7 +34,7 @@
 The option ``-Wl,-rpath,<libcxx-install-prefix>/lib`` adds a runtime library
 search path. Meaning that the systems dynamic linker will look for libc++ in
 ``<libcxx-install-prefix>/lib`` whenever the program is run. Alternatively the
-environment variable ``LD_LIBRARY_PATH`` (``DYLD_LIBRARY_PATH`` on OS X) can
+environment variable ``LD_LIBRARY_PATH`` (``DYLD_LIBRARY_PATH`` on macOS) can
 be used to change the dynamic linkers search paths after a program is compiled.
 An example of using ``LD_LIBRARY_PATH``:
diff --git a/docs/index.rst b/docs/index.rst
index 0fd3540..933d0fe 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -93,7 +93,7 @@
 ============ ==================== ============ ========================
 OS           Arch                 Compilers    ABI Library
 ============ ==================== ============ ========================
-Mac OS X     i386, x86_64         Clang, GCC   libc++abi
+macOS        i386, x86_64         Clang, GCC   libc++abi
 FreeBSD 10+  i386, x86_64, ARM    Clang, GCC   libcxxrt, libc++abi
 Linux        i386, x86_64         Clang, GCC   libc++abi
 ============ ==================== ============ ========================