rust: Fix install_gentoo instructions

rust/install_gentoo.txt

@@ -2,7 +2,8 @@ ver=<ver>
 sudo rsync -rvP build/install-rustc-$ver/ /opt/rust-bin-$ver
 
 sudo emerge -1 app-eselect/eselect-rust
-sudo ln -s /opt/rust-bin-$ver/bin/rustc /usr/bin/rustc-bin-$ver
+sudo cp /opt/rust-bin-$ver/bin/rustc /opt/rust-bin-$ver/bin/rustc-bin-$ver
+sudo ln -s /opt/rust-bin-$ver/bin/rustc-bin-$ver /usr/bin/rustc-bin-$ver
 sudo mkdir -p /etc/env.d/rust
 sudo touch /etc/env.d/rust/provider-rust-bin-$ver
 sudo eselect rust set rust-bin-$ver
@@ -10,7 +11,6 @@ sudo mkdir -p /var/db/pkg/dev-lang/rust-bin-$ver
 echo 0 | sudo tee /var/db/pkg/dev-lang/rust-bin-$ver/SLOT > /dev/null
 
 sudo emerge dev-lang/rust
-(might need to set CC=clang and CXX=clang++ for initial build...)
 
 sudo rm -rf /opt/rust-bin-$ver /usr/bin/rustc-bin-$ver
 sudo rm -rf /etc/env.d/rust/provider-rust-bin-$ver