hack: compile w/o optimizations & inlining when debugging

Without these compile flags, Delve is unable to report the value of some
variables and it's not possible to jump into inlined code.

As the contributing docs already mention that `DOCKER_DEBUG` should
disable "build optimizations", the env var is reused here instead of
introducing a new one.

Signed-off-by: Albin Kerouanton <albinker@gmail.com>

hack/make/.binary

@@ -74,11 +74,15 @@ source "${MAKEDIR}/.go-autogen"
 		fi
 	fi
 
+	if [ -n "${DOCKER_DEBUG}" ]; then
+		GCFLAGS="all=-N -l"
+	fi
+
 	echo "Building $([ "$DOCKER_STATIC" = "1" ] && echo "static" || echo "dynamic") $DEST/$BINARY_FULLNAME ($PLATFORM_NAME)..."
 	if [ -n "$DOCKER_DEBUG" ]; then
 		set -x
 	fi
-	./hack/with-go-mod.sh go build -mod=vendor -modfile=vendor.mod -o "$DEST/$BINARY_FULLNAME" "${BUILDFLAGS[@]}" -ldflags "$LDFLAGS $LDFLAGS_STATIC $DOCKER_LDFLAGS" "$GO_PACKAGE"
+	./hack/with-go-mod.sh go build -mod=vendor -modfile=vendor.mod -o "$DEST/$BINARY_FULLNAME" "${BUILDFLAGS[@]}" -ldflags "$LDFLAGS $LDFLAGS_STATIC $DOCKER_LDFLAGS" -gcflags="${GCFLAGS}" "$GO_PACKAGE"
 )
 
 echo "Created binary: $DEST/$BINARY_FULLNAME"