Ensure warnings cause build failures in CI

.github/workflows/ci.yml

@@ -10,6 +10,7 @@ env:
   CARGO_TERM_COLOR: always
   PNET_FEATURES: travis pcap serde
   PNET_MACROS_FEATURES: travis
+  VERBOSE: 1
 
 jobs:
   build-ubuntu:

build.sh

@@ -23,13 +23,13 @@ MACROS_WITH_SYNTEX=0
 if [[ -n "$PNET_FEATURES" ]]; then
     PNET_CARGO_FLAGS="--no-default-features --features \"$PNET_FEATURES\""
 else
-    PNET_CARGO_FLAGS=
+    PNET_CARGO_FLAGS=""
 fi
 
 if [[ -n "$PNET_MACROS_FEATURES" ]]; then
     PNET_MACROS_CARGO_FLAGS="--no-default-features --features \"$PNET_MACROS_FEATURES\""
 else
-    PNET_MACROS_CARGO_FLAGS=
+    PNET_MACROS_CARGO_FLAGS=""
 fi
 
 # FIXME Need to get interface differently on Windows
@@ -38,6 +38,8 @@ IPROUTE2=$(which ip)
 
 echo $PNET_MACROS_FEATURES | grep -q with-syntex && MACROS_WITH_SYNTEX=1
 
+PNET_TEST_IFACE=""
+
 if [[ -x "$IFCONFIG" ]]; then
     PNET_TEST_IFACE=$($IFCONFIG | egrep 'UP| active' | \
                       perl -pe '/^[A-z0-9]+:([^\n]|\n\t)*status: active/' | \
@@ -60,6 +62,8 @@ if [[ -z "$PNET_TEST_IFACE" && "$SYSTEM" = "Linux" ]]; then
     done
 fi
 
+set -euo pipefail
+
 # FIXME Need to link libraries properly on Windows
 build() {
     if [[ -x "$CARGO" ]]; then