RISC-V: fix docker image creation for CI cross-builds

This commit fixes Dockerfile creating image for RISC-V CI builds. The
problem was that URL libfakeroot and libfakechroot was no longer valid.
It pointed to Debian ports archive, but meanwhile RISC-V architecture
became "officially" supported (will be once Trixie is out).

It is not clear to me why Dockerfile downloaded and extracted RISC-V
versions of libfakeroot and libfakechroot at all. However, I had been
successfully building sysroots for OMR and/or OpenJ9 compilations using

    mmdebstrap --mode=fakeroot --variant=extract

without need of RISC-V libfakeroot and libfakechroot. So this commit
removes download and manual installation of them and uses
--variant=extract to build sysroot. In addition it uses new ("official")
Debian archives to build the sysroot. This way the aforementioned
problem with outdated URLs should be fixed for good.

Fixes eclipse-omr#7256.

buildenv/docker/riscv64/debian11/Dockerfile

@@ -74,24 +74,13 @@ RUN gpg --homedir /tmp \
         --export 8D69674688B6CB36 > /etc/apt/trusted.gpg.d/debian-ports-archive-2023.gpg
 
 # Install RISC-V 64 build root in /opt/sysroot
-RUN apt-get install -y fakeroot
-RUN wget -O /tmp/libfakeroot_1.31-1.2_riscv64.deb \
-	 http://ftp.ports.debian.org/debian-ports/pool-riscv64/main/f/fakeroot/libfakeroot_1.31-1.2_riscv64.deb
-RUN wget -O /tmp/libfakechroot_2.20.1+ds-15_riscv64.deb \
-	http://ftp.ports.debian.org/debian-ports/pool-riscv64/main/f/fakechroot/libfakechroot_2.20.1+ds-15_riscv64.deb
-RUN dpkg -X /tmp/libfakeroot_1.31-1.2_riscv64.deb /
-RUN dpkg -X /tmp/libfakechroot_2.20.1+ds-15_riscv64.deb /
-
-RUN update-alternatives --set  fakeroot /usr/bin/fakeroot-tcp
-
 RUN mmdebstrap \
 	--mode=fakeroot \
-	--variant=minbase \
+	--variant=extract \
 	--architectures=riscv64 \
 	--include="debian-ports-archive-keyring,build-essential,libdwarf-dev,libelf-dev,libx11-dev,libxext-dev,libxrender-dev,libxrandr-dev,libxtst-dev,libxt-dev,libasound2-dev,libcups2-dev,libfontconfig1-dev" \
-	bullseye "/opt/sysroot" \
-	"deb http://deb.debian.org/debian-ports/ sid main" \
-	"deb http://deb.debian.org/debian-ports/ unreleased main"
+	unstable "/opt/sysroot" \
+	"deb http://deb.debian.org/debian unstable main contrib"
 
 ENV CROSS_SYSROOT_RISCV64=/opt/sysroot
 USER jenkins