fixed #4179 bin/flutter fails when linked with relative symlink (#4196)

* fixed issue #4179 bin/flutter fails when linked with relative symlink

* fixed issue #4179 bin/flutter fails when linked with relative symlink

* My second attempt at following symlinks correctly

bin/flutter

@@ -6,12 +6,16 @@
 set -e
 
 function follow_links() {
-  file="$1"
+  cd -P "${1%/*}"
+  file="$PWD/${1##*/}"
   while [ -h "$file" ]; do
     # On Mac OS, readlink -f doesn't work.
+    cd -P "${file%/*}"
     file="$(readlink "$file")"
+    cd -P "${file%/*}"
+    file="$PWD/${file##*/}"
   done
-  echo "$file"
+  echo "$PWD/${file##*/}"
 }
 
 PROG_NAME="$(follow_links "$BASH_SOURCE")"