tools: bootstrap: add support for symlinks in pwd (envoyproxy#22513)

Currently bootstrap does not support paths with symlinks.

For example:

ln -s envoy/ envoy-symlink
cd envoy-symlink
support/bootstrap
ERROR: this script must be run at the root of the envoy source tree

$ echo $PWD
/envoy-symlink
$ echo "$(git rev-parse --show-toplevel)"
/envoy

Solution is to use pwd -P (physical: avoid all symlinks) instead of $PWD

$ echo "$(pwd -P)"
/envoy

Signed-off-by: Ruslan Mstoi <[email protected]>

Author: Ruslan Mstoi

support/bootstrap

@@ -9,7 +9,7 @@
 # TODO(hausdorff): If compatibility becomes an issue here, come back and do this
 # "the right way". This is hard to do in general, since `realpath` is not
 # standard.
-if [ ! "$PWD" == "$(git rev-parse --show-toplevel)" ]; then
+if [ ! "$(pwd -P)" == "$(git rev-parse --show-toplevel)" ]; then
     cat >&2 <<__EOF__
 ERROR: this script must be run at the root of the envoy source tree
 __EOF__