Accept `GIT_VERSION=` environment variable

In some environments it is impossible to unset
environment variable, and no `GIT_VERSION=` works.

This allows to pass empty value that indicates
that a default should be used. For example allowing
to execute: `make git GIT_VERSION=`.

Changelog: fixed

1 files changed, 1 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index dc3f869bf..16f4acd94 100644
--- a/Makefile
+++ b/Makefile
@@ -85,7 +85,7 @@ LIBGIT2_VERSION           ?= v1.2.0
 
 # Support both vX.Y.Z and X.Y.Z version patterns, since callers across
 # GitLab use both.
-ifeq ($(origin GIT_VERSION),undefined)
+ifeq (,$(GIT_VERSION))
   GIT_VERSION := v2.33.1
 else
   GIT_VERSION := $(shell echo ${GIT_VERSION} | awk '/^[0-9]\.[0-9]+\.[0-9]+$$/ { printf "v" } { print $$1 }')