8280863: Update build README to reflect that MSYS2 is supported

Reviewed-by: clanger
Backport-of: 6de90ad9800b83c4a5f364c3645603fcb6828d6c

doc/building.html

@@ -195,7 +195,7 @@ <h2 id="operating-system-requirements">Operating System Requirements</h2>
 <h3 id="windows">Windows</h3>
 <p>Windows XP is not a supported platform, but all newer Windows should be able to build the JDK.</p>
 <p>On Windows, it is important that you pay attention to the instructions in the <a href="#special-considerations">Special Considerations</a>.</p>
-<p>Windows is the only non-POSIX OS supported by the JDK, and as such, requires some extra care. A POSIX support layer is required to build on Windows. Currently, the only supported such layers are Cygwin and Windows Subsystem for Linux (WSL). (Msys is no longer supported due to a too old bash; msys2 would likely be possible to support in a future version but that would require effort to implement.)</p>
+<p>Windows is the only non-POSIX OS supported by the JDK, and as such, requires some extra care. A POSIX support layer is required to build on Windows. Currently, the only supported such layers are Cygwin, Windows Subsystem for Linux (WSL), and MSYS2. (MSYS is no longer supported due to an outdated bash; While OpenJDK can be built with MSYS2, support for it is still experimental, so build failures and unusual errors are not uncommon.)</p>
 <p>Internally in the build system, all paths are represented as Unix-style paths, e.g. <code>/cygdrive/c/git/jdk/Makefile</code> rather than <code>C:\git\jdk\Makefile</code>. This rule also applies to input to the build system, e.g. in arguments to <code>configure</code>. So, use <code>--with-msvcr-dll=/cygdrive/c/msvcr100.dll</code> rather than <code>--with-msvcr-dll=c:\msvcr100.dll</code>. For details on this conversion, see the section on <a href="#fixpath">Fixpath</a>.</p>
 <h4 id="cygwin">Cygwin</h4>
 <p>A functioning <a href="http://www.cygwin.com/">Cygwin</a> environment is required for building the JDK on Windows. If you have a 64-bit OS, we strongly recommend using the 64-bit version of Cygwin.</p>
@@ -297,7 +297,7 @@ <h3 id="apple-xcode">Apple Xcode</h3>
 <p>It is advisable to keep an older version of Xcode for building the JDK when updating Xcode. This <a href="http://iosdevelopertips.com/xcode/install-multiple-versions-of-xcode.html">blog page</a> has good suggestions on managing multiple Xcode versions. To use a specific version of Xcode, use <code>xcode-select -s</code> before running <code>configure</code>, or use <code>--with-toolchain-path</code> to point to the version of Xcode to use, e.g. <code>configure --with-toolchain-path=/Applications/Xcode8.app/Contents/Developer/usr/bin</code></p>
 <p>If you have recently (inadvertently) updated your OS and/or Xcode version, and the JDK can no longer be built, please see the section on <a href="#problems-with-the-build-environment">Problems with the Build Environment</a>, and <a href="#getting-help">Getting Help</a> to find out if there are any recent, non-merged patches available for this update.</p>
 <h3 id="microsoft-visual-studio">Microsoft Visual Studio</h3>
-<p>The minimum accepted version of Visual Studio is 2017. Older versions will not be accepted by <code>configure</code> and will not work. The maximum accepted version of Visual Studio is 2019.</p>
+<p>For aarch64 machines running Windows the minimum accepted version is Visual Studio 2019 (16.8 or higher). For all other platforms the minimum accepted version of Visual Studio is 2017. Older versions will not be accepted by <code>configure</code> and will not work. For all platforms the maximum accepted version of Visual Studio is 2019.</p>
 <p>If you have multiple versions of Visual Studio installed, <code>configure</code> will by default pick the latest. You can request a specific version to be used by setting <code>--with-toolchain-version</code>, e.g. <code>--with-toolchain-version=2017</code>.</p>
 <p>If you have Visual Studio installed but <code>configure</code> fails to detect it, it may be because of <a href="#spaces-in-path">spaces in path</a>.</p>
 <h3 id="ibm-xl-cc">IBM XL C/C++</h3>

doc/building.md

@@ -179,10 +179,10 @@ On Windows, it is important that you pay attention to the instructions in the
 
 Windows is the only non-POSIX OS supported by the JDK, and as such, requires
 some extra care. A POSIX support layer is required to build on Windows.
-Currently, the only supported such layers are Cygwin and Windows Subsystem for
-Linux (WSL). (Msys is no longer supported due to a too old bash; msys2 would
-likely be possible to support in a future version but that would require effort
-to implement.)
+Currently, the only supported such layers are Cygwin, Windows Subsystem for
+Linux (WSL), and MSYS2. (MSYS is no longer supported due to an outdated bash;
+While OpenJDK can be built with MSYS2, support for it is still experimental, so
+build failures and unusual errors are not uncommon.)
 
 Internally in the build system, all paths are represented as Unix-style paths,
 e.g. `/cygdrive/c/git/jdk/Makefile` rather than `C:\git\jdk\Makefile`. This