[llvm][Docs] Update supported hardware (llvm#121743)

Since someone on Discord asked why macOS arm64 was not listed.

https://llvm.org/docs/GettingStarted.html#hardware

Add a few known platforms:
* Linux AArch64
* FreeBSD AArch64
* macOS arm64 (Clang build only, there might be a GCC port but I've not
used it myself)
* Windows on Arm (ARM64 as Microsoft refers to it)

Author: DavidSpickett

llvm/docs/GettingStarted.rst

@@ -233,36 +233,42 @@ Hardware
 
 LLVM is known to work on the following host platforms:
 
-================== ===================== =============
+================== ===================== ==============================
 OS                 Arch                  Compilers
-================== ===================== =============
+================== ===================== ==============================
 Linux              x86\ :sup:`1`         GCC, Clang
 Linux              amd64                 GCC, Clang
 Linux              ARM                   GCC, Clang
+Linux              AArch64               GCC, Clang
 Linux              Mips                  GCC, Clang
 Linux              PowerPC               GCC, Clang
 Linux              SystemZ               GCC, Clang
 Solaris            V9 (Ultrasparc)       GCC
 DragonFlyBSD       amd64                 GCC, Clang
 FreeBSD            x86\ :sup:`1`         GCC, Clang
 FreeBSD            amd64                 GCC, Clang
+FreeBSD            AArch64               GCC, Clang
 NetBSD             x86\ :sup:`1`         GCC, Clang
 NetBSD             amd64                 GCC, Clang
 OpenBSD            x86\ :sup:`1`         GCC, Clang
 OpenBSD            amd64                 GCC, Clang
 macOS\ :sup:`2`    PowerPC               GCC
 macOS              x86                   GCC, Clang
+macOS              arm64                 Clang
 Cygwin/Win32       x86\ :sup:`1, 3`      GCC
 Windows            x86\ :sup:`1`         Visual Studio
-Windows x64        x86-64                Visual Studio
-================== ===================== =============
+Windows x64        x86-64                Visual Studio, Clang\ :sup:`4`
+Windows on Arm     ARM64                 Visual Studio, Clang\ :sup:`4`
+================== ===================== ==============================
 
 .. note::
 
   #. Code generation supported for Pentium processors and up
   #. Code generation supported for 32-bit ABI only
   #. To use LLVM modules on Win32-based system, you may configure LLVM
      with ``-DBUILD_SHARED_LIBS=On``.
+  #. Visual Studio alone can compile LLVM. When using Clang, you
+     must also have Visual Studio installed.
 
 Note that Debug builds require a lot of time and disk space.  An LLVM-only build
 will need about 1-3 GB of space.  A full build of LLVM and Clang will need around