Remove --build option per comment indicating it is not preferred

See openjdk#24267 (comment)

Author: swesonga

doc/building.html

@@ -1723,13 +1723,6 @@ <h4 id="building-for-musl">Building for musl</h4>
 --with-sysroot=$SYSROOT</code></pre>
 <p>and run <code>make</code> normally.</p>
 <h4 id="building-for-windows-aarch64">Building for Windows AArch64</h4>
-<p>To generate Windows AArch64 builds using Cygwin on a Windows AArch64
-machine, use the <code>--build</code> option to specify a native build
-(this argument is required because the machine type supported by Cygwin
-is x86_64):</p>
-<pre><code>bash configure \
-  --with-boot-jdk=$BOOT_JDK \
-  --build=aarch64-unknown-cygwin</code></pre>
 <p>To generate Windows AArch64 builds using Cygwin on a Windows x64
 machine, the target platform needs to be set to
 <code>aarch64-unknown-cygwin</code> to enable cross compilation.

doc/building.md

@@ -1459,16 +1459,6 @@ and run `make` normally.
 
 #### Building for Windows AArch64
 
-To generate Windows AArch64 builds using Cygwin on a Windows AArch64 machine,
-use the `--build` option to specify a native build (this argument is required
-because the machine type supported by Cygwin is x86_64):
-
-```
-bash configure \
-  --with-boot-jdk=$BOOT_JDK \
-  --build=aarch64-unknown-cygwin
-```
-
 To generate Windows AArch64 builds using Cygwin on a Windows x64 machine,
 the target platform needs to be set to `aarch64-unknown-cygwin` to enable
 cross compilation. Configure the build with `--openjdk-target`: