Clarify notes why Highway is not compiled on specific targets (#286)

Author: kleisauke

platforms/linux-riscv64/Dockerfile

@@ -48,6 +48,9 @@ ENV \
   RUST_TARGET="riscv64gc-unknown-linux-gnu" \
   FLAGS="-march=rv64gc" \
   RUSTFLAGS="-Zlocation-detail=none -Zfmt-debug=none" \
+  # Highway requires RVV version 1.0, which isn't the baseline
+  # in Debian yet. Therefore, it should remain disabled for now.
+  #FLAGS="-march=rv64gcv1p0 -menable-experimental-extensions" \
   WITHOUT_HIGHWAY="true" \
   MESON="--cross-file=/root/meson.ini"
 

platforms/linux-s390x/Dockerfile

@@ -52,9 +52,8 @@ ENV \
   RUST_TARGET="s390x-unknown-linux-gnu" \
   FLAGS="" \
   RUSTFLAGS="-Zlocation-detail=none -Zfmt-debug=none" \
-  # Highway supports IBMZ starting from IBM/Z14, which needs GCC 11 or
-  # higher (i.e. Debian 12, glibc 2.36). Therefore, it should be disabled
-  # for the time being.
+  # Highway requires IBM z14, which isn't the baseline in
+  # Debian yet. Therefore, it should remain disabled for now.
   #FLAGS="-march=z14 -mzvector" \
   WITHOUT_HIGHWAY="true" \
   MESON="--cross-file=/root/meson.ini"