fix(build): derive xgo image tag from GO_VERSION

The Go version was pinned in three places and #422 updated only two:
native/go.mod, GO_VERSION in the workflows, and the hardcoded xgo
image tag here (left at go-1.25.10).

Once go.mod requires go >= 1.26.0, the toolchain inside the
go-1.25.10 container auto-downloads Go 1.26.0 and runs its linker
against that image's older GNU binutils, which cannot parse the .def
file Go 1.26 emits. The Windows DLL then fails to link and the
enforcer reports the missing file as the symptom.

Deriving the tag from GO_VERSION removes the drift: CI already
exports it, and make's `?=` prefers the environment value.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Marc Nuri <marc@marcnuri.com>

Author: manusa

Makefile

@@ -4,6 +4,13 @@
 .DEFAULT_GOAL := help
 
 CGO_ENABLED = 1
+# Go toolchain version. CI exports GO_VERSION (see .github/workflows/*.yml), which
+# overrides this default, so the two cannot drift apart.
+# The xgo image must ship a Go >= the `go` directive in native/go.mod. Otherwise the
+# container silently downloads a newer toolchain whose linker is incompatible with
+# that image's mingw-w64 binutils, and the Windows DLL fails to link.
+GO_VERSION ?= 1.26.7
+XGO_IMAGE = ghcr.io/techknowlogick/xgo:go-$(GO_VERSION)
 LD_FLAGS = -s -w
 COMMON_BUILD_ARGS = -ldflags "$(LD_FLAGS)" -buildmode=c-shared
 MAVEN_OPTIONS =
@@ -59,7 +66,7 @@ build-native: ## Build the native shared library for the current platform
 .PHONY: build-native-cross-platform
 build-native-cross-platform: ## Build native shared libraries for all 5 supported platforms (requires Docker)
 	go install src.techknowlogick.com/xgo@latest
-	xgo -image ghcr.io/techknowlogick/xgo:go-1.25.10 $(COMMON_BUILD_ARGS) -out native/out/helm --targets */arm64,*/amd64 ./native
+	xgo -image $(XGO_IMAGE) $(COMMON_BUILD_ARGS) -out native/out/helm --targets */arm64,*/amd64 ./native
 
 .PHONY: build-java
 build-java: ## Build and verify the Java artifacts (mvn clean verify)