Toolchain+Ports: Install host ruby into Local/ruby, not Local/$ARCH

Following the pattern for qemu, mold, and clang, we should install the
host ruby required to build the ruby port into its own install tree
rather than forcing it into the GNU compiler's bindir.

Ports/ruby/package.sh

@@ -2,6 +2,8 @@
 
 source version.sh
 
+export PATH="${SERENITY_SOURCE_DIR}/Toolchain/Local/ruby/bin:${PATH}"
+
 port=ruby
 version=${RUBY_VERSION}
 useconfigure="true"

Toolchain/BuildRuby.sh

@@ -5,9 +5,8 @@ set -e
 
 DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 
-ARCH=${ARCH:-"i686"}
-PREFIX_DIR="$DIR/Local/$ARCH"
-BUILD_DIR="$DIR/Build/$ARCH"
+PREFIX_DIR="$DIR/Local/ruby"
+BUILD_DIR="$DIR/Build/ruby"
 TARBALLS_DIR="$DIR/Tarballs"
 
 # shellcheck source=/dev/null
@@ -42,9 +41,9 @@ if [ -z "$MAKEJOBS" ]; then
 fi
 
 mkdir -p "${PREFIX_DIR}"
-mkdir -p "${BUILD_DIR}/ruby"
+mkdir -p "${BUILD_DIR}"
 
-pushd "${BUILD_DIR}/ruby"
+pushd "${BUILD_DIR}"
     "${TARBALLS_DIR}"/ruby-"${RUBY_VERSION}"/configure --prefix="${PREFIX_DIR}"
     make -j "${MAKEJOBS}"
     make install