While adapting my CI to build hsdis automatically, I realized that sometimes we miss the proper $AR for binutils cross-build. Configure would then fail like:

```
$ CXX=aarch64-linux-gnu-g++ CC=aarch64-linux-gnu-gcc sh ./configure --with-debug-level=fastdebug --openjdk-target=aarch64-linux-gnu --with-sysroot=/chroots/arm64 --with-boot-jdk=/home/shade/Install/jdk19u-ea --with-hsdis=binutils --with-binutils-src=binutils-2.38
...
/usr/bin/bash: line 1: aarch64-unknown-linux-gnu-ar: command not found
gmake[1]: *** [Makefile:254: libiberty.a] Error 127
gmake[1]: Leaving directory '/home/shade/trunks/jdk/build/linux-aarch64-server-fastdebug/configure-support/binutils/libiberty'
gmake: *** [Makefile:9220: all-libiberty] Error 2
configure: Automatic building of binutils failed on make. Try building it manually
configure: error: Cannot continue
configure exiting with result code 1
```