build: don't assume git repo in make_packages.sh

to be able to run it from an unpacked sdist

contrib/make_packages.sh

@@ -8,6 +8,7 @@ PROJECT_ROOT="$CONTRIB"/..
 PACKAGES="$PROJECT_ROOT"/packages/
 
 test -n "$CONTRIB" -a -d "$CONTRIB" || exit
+cd "$CONTRIB"
 
 if [ -d "$PACKAGES" ]; then
     rm -r "$PACKAGES"
@@ -21,7 +22,7 @@ python3 -m venv "$venv_dir"
 source "$venv_dir"/bin/activate
 
 # installing pinned build-time requirements, such as pip/wheel/setuptools
-python -m pip install --no-build-isolation --no-dependencies --no-warn-script-location \
+python3 -m pip install --no-build-isolation --no-dependencies --no-warn-script-location \
     -r "$CONTRIB"/deterministic-build/requirements-build-base.txt
 
 # opt out of compiling C extensions
@@ -34,7 +35,7 @@ export FROZENLIST_NO_EXTENSIONS=1
 # if we end up having to compile something, at least give reproducibility a fighting chance
 export LC_ALL=C
 export TZ=UTC
-export SOURCE_DATE_EPOCH="$(git log -1 --pretty=%ct)"
+export SOURCE_DATE_EPOCH="$(git log -1 --pretty=%ct 2>/dev/null || printf 1530212462)"
 export PYTHONHASHSEED="$SOURCE_DATE_EPOCH"
 export BUILD_DATE="$(LC_ALL=C TZ=UTC date +'%b %e %Y' -d @$SOURCE_DATE_EPOCH)"
 export BUILD_TIME="$(LC_ALL=C TZ=UTC date +'%H:%M:%S' -d @$SOURCE_DATE_EPOCH)"
@@ -49,4 +50,4 @@ export BUILD_TIME="$(LC_ALL=C TZ=UTC date +'%H:%M:%S' -d @$SOURCE_DATE_EPOCH)"
 # note: --no-build-isolation is needed so that pip uses the locally available setuptools and wheel,
 #       instead of downloading the latest ones
 python3 -m pip install --no-build-isolation --no-compile --no-dependencies --no-binary :all: \
-    -r "$CONTRIB"/deterministic-build/requirements.txt -t "$CONTRIB"/../packages
+    -r "$CONTRIB"/deterministic-build/requirements.txt -t "$PACKAGES"