fix(test): enable CGO cross-compilation for plugin support on macOS

The local-image and install targets cross-compiled the dgraph binary
without CGO, producing a statically linked binary that cannot dlopen()
Go plugin .so files. This caused all plugin tests to fail on macOS
with "Invalid tokenizer anagram".

Changes:
- Add LINUX_CC variable for architecture-aware cross-compiler selection
- Enable CGO_ENABLED=1 with cross-compiler in install and local-image
- Use BFD linker (-fuse-ld=bfd) since gold is not in cross-toolchains
- Skip jemalloc (BUILD_TAGS=) for cross-compilation (headers unavailable)
- Add EXTLDFLAGS support to dgraph/Makefile for external linker flags
- Split t/Makefile check into deps (tools) + check (tools + binary)
- Top-level setup now calls t/deps so it no longer requires the binary

Author: mlwelles

Makefile

@@ -18,11 +18,20 @@ ifeq ($(GOPATH),)
     $(error GOPATH is not set. Please set it explicitly, e.g. export GOPATH=$$HOME/go)
 endif
 
-# On non-Linux systems, use a separate directory for Linux binaries
+# On non-Linux systems, use a separate directory for Linux binaries and
+# a cross-compiler so that CGO is available (required for plugin support).
 ifeq ($(GOHOSTOS),linux)
     export LINUX_GOBIN ?= $(GOPATH)/bin
+    LINUX_CC          ?= gcc
 else
     export LINUX_GOBIN ?= $(GOPATH)/linux_$(GOHOSTARCH)
+    ifeq ($(GOHOSTARCH),arm64)
+        LINUX_CC ?= aarch64-unknown-linux-gnu-gcc
+    else ifeq ($(GOHOSTARCH),amd64)
+        LINUX_CC ?= x86_64-unknown-linux-gnu-gcc
+    else
+        LINUX_CC ?= gcc
+    endif
 endif
 
 ######################
@@ -60,7 +69,7 @@ install: ## Install dgraph binary
 ifneq ($(GOHOSTOS),linux)
 	@mkdir -p $(LINUX_GOBIN)
 	@echo "Installing dgraph (linux/$(GOHOSTARCH))..."
-	@GOOS=linux GOARCH=$(GOHOSTARCH) $(MAKE) -C dgraph dgraph
+	@GOOS=linux GOARCH=$(GOHOSTARCH) CGO_ENABLED=1 CC=$(LINUX_CC) $(MAKE) -C dgraph BUILD_TAGS= EXTLDFLAGS=-fuse-ld=bfd dgraph
 	@mv dgraph/dgraph $(LINUX_GOBIN)/dgraph
 	@echo "Installed dgraph (linux/$(GOHOSTARCH)) to $(LINUX_GOBIN)/dgraph"
 endif
@@ -80,7 +89,7 @@ dgraph-installed:
 
 .PHONY: deps
 deps: ## Check test dependencies (pass AUTO_INSTALL=true to auto-install missing ones)
-	$(MAKE) -C t check
+	$(MAKE) -C t deps
 
 .PHONY: setup
 setup: ## Install all test dependencies automatically
@@ -181,7 +190,11 @@ test-benchmark: ## Go benchmarks (i.e. 'go test -bench')
 .PHONY: local-image
 local-image: ## Build local Docker image (dgraph/dgraph:local)
 	@echo building local docker image
-	@GOOS=linux GOARCH=amd64 $(MAKE) dgraph
+ifneq ($(GOHOSTOS),linux)
+	@GOOS=linux GOARCH=$(GOHOSTARCH) CGO_ENABLED=1 CC=$(LINUX_CC) $(MAKE) BUILD_TAGS= EXTLDFLAGS=-fuse-ld=bfd dgraph
+else
+	@GOOS=linux GOARCH=$(GOHOSTARCH) $(MAKE) dgraph
+endif
 	@mkdir -p linux
 	@mv ./dgraph/dgraph ./linux/dgraph
 	@docker build -f contrib/Dockerfile -t dgraph/dgraph:local .

dgraph/Makefile

@@ -32,7 +32,8 @@ gitBranch       = github.com/dgraph-io/dgraph/v25/x.gitBranch
 lastCommitSHA   = github.com/dgraph-io/dgraph/v25/x.lastCommitSHA
 lastCommitTime  = github.com/dgraph-io/dgraph/v25/x.lastCommitTime
 
-BUILD_FLAGS   ?= -ldflags '-X ${lastCommitSHA}=${BUILD} -X "${lastCommitTime}=${BUILD_DATE}" -X "${dgraphVersion}=${BUILD_VERSION}" -X "${dgraphCodename}=${BUILD_CODENAME}" -X ${gitBranch}=${BUILD_BRANCH}'
+EXTLDFLAGS    ?=
+BUILD_FLAGS   ?= -ldflags '-X ${lastCommitSHA}=${BUILD} -X "${lastCommitTime}=${BUILD_DATE}" -X "${dgraphVersion}=${BUILD_VERSION}" -X "${dgraphCodename}=${BUILD_CODENAME}" -X ${gitBranch}=${BUILD_BRANCH}$(if $(EXTLDFLAGS), -extldflags "$(EXTLDFLAGS)")'
 
 # Insert build tags if specified
 ifneq ($(strip $(BUILD_TAGS)),)

t/Makefile

@@ -18,12 +18,15 @@ endif
 
 all: test
 
-.PHONY: check
-check: check-go check-docker check-gotestsum check-ack check-cross-compiler
+.PHONY: deps
+deps: check-go check-docker check-gotestsum check-ack check-cross-compiler
 	@if [ "$(GOOS)" = "linux" ]; then \
 		which protoc > /dev/null 2>&1 || (echo "Error: protoc is not installed or not in PATH" && exit 1); \
 	fi
 	@echo "All dependencies are installed"
+
+.PHONY: check
+check: deps
 	@echo "LINUX_GOBIN=$(LINUX_GOBIN)"
 	@if [ -f "$(LINUX_GOBIN)/dgraph" ]; then \
 		file $(LINUX_GOBIN)/dgraph | grep -q "ELF.*executable" || (echo "Error: dgraph binary at $(LINUX_GOBIN)/dgraph is not a Linux executable" && exit 1); \