fix: make sure the displayed commit hash is right

Don't display the commit hash the submodule should have, but the one the
actual directory has. This allows replacing the `rust-fil-sector-builder`
with a symlink to a local version.

install-rust-fil-sector-builder

@@ -28,7 +28,6 @@ if [ -z "$(ls -A $subm_dir)" ]; then
 fi
 
 # Directory is not empty, hence compiling whatever source is in there
-(>&2 echo "building ${subm_dir} from source")
 build_from_source "${subm_dir}"
 
 mkdir -p include

install-shared.bash

@@ -44,10 +44,10 @@ download_release_tarball() {
 
 build_from_source() {
     __submodule_path=$1
-    __submodule_sha1=$(git rev-parse @:"${__submodule_path}")
+    __submodule_sha1=$(cd ${__submodule_path} && git rev-parse @)
     __submodule_sha1_truncated="${__submodule_sha1:0:16}"
 
-    echo "building from source @ ${__submodule_sha1_truncated}"
+    echo "building ${__submodule_path} from source @ ${__submodule_sha1_truncated}"
 
     if ! [ -x "$(command -v cargo)" ]; then
         (>&2 echo 'Error: cargo is not installed.')