env: update environment variable paths to use realpath.

Update the environment variable path so that source env.sh can be "source" in any folder.

Author: zephyrols

env.sh

@@ -1,10 +1,11 @@
 # This script will setup XiangShan environment variables
 
-export XS_PROJECT_ROOT=$(pwd)
-export NEMU_HOME=$(pwd)/NEMU
-export AM_HOME=$(pwd)/nexus-am
-export NOOP_HOME=$(pwd)/XiangShan
-export DRAMSIM3_HOME=$(pwd)/DRAMsim3
+SCRIPT_PATH="${BASH_SOURCE[0]:-$0}"
+export XS_PROJECT_ROOT=$(dirname $(realpath ${SCRIPT_PATH}))
+export NEMU_HOME=$XS_PROJECT_ROOT/NEMU
+export AM_HOME=$XS_PROJECT_ROOT/nexus-am
+export NOOP_HOME=$XS_PROJECT_ROOT/XiangShan
+export DRAMSIM3_HOME=$XS_PROJECT_ROOT/DRAMsim3
 
 echo SET XS_PROJECT_ROOT: ${XS_PROJECT_ROOT}
 echo SET NOOP_HOME \(XiangShan RTL Home\): ${NOOP_HOME}