Revert "add a better variable override mechanism"

This reverts commit f56b186.

Author: stanislav-zaprudskiy

Makefile

@@ -52,11 +52,11 @@ prepare-static-check: FORCE install-golangci-lint install-modernize install-shel
 
 # To add additional flags or values, specify the variable in the environment, e.g. `GO_BUILDFLAGS='-tags experimental' make`.
 # To override the default flags or values, specify the variable on the command line, e.g. `make GO_BUILDFLAGS='-tags experimental'`.
-GO_BUILDFLAGS += -mod vendor
-GO_LDFLAGS +=
-GO_TESTFLAGS +=
-GO_TESTENV +=
-GO_BUILDENV +=
+GO_BUILDFLAGS := -mod vendor $(GO_BUILDFLAGS)
+GO_LDFLAGS := $(GO_LDFLAGS)
+GO_TESTFLAGS := $(GO_TESTFLAGS)
+GO_TESTENV := $(GO_TESTENV)
+GO_BUILDENV := $(GO_BUILDENV)
 
 # These definitions are overridable, e.g. to provide fixed version/commit values when
 # no .git directory is present or to provide a fixed build date for reproducibility.

internal/makefile/makefile.go

@@ -213,11 +213,11 @@ endif
 	if isGolang {
 		build.addDefinition("# To add additional flags or values, specify the variable in the environment, e.g. `GO_BUILDFLAGS='-tags experimental' make`.")
 		build.addDefinition("# To override the default flags or values, specify the variable on the command line, e.g. `make GO_BUILDFLAGS='-tags experimental'`.")
-		build.addDefinition("GO_BUILDFLAGS +=%s", cfg.Variable("GO_BUILDFLAGS", defaultBuildFlags))
-		build.addDefinition("GO_LDFLAGS +=%s", cfg.Variable("GO_LDFLAGS", strings.TrimSpace(defaultLdFlags)))
-		build.addDefinition("GO_TESTFLAGS +=%s", cfg.Variable("GO_TESTFLAGS", ""))
-		build.addDefinition("GO_TESTENV +=%s", cfg.Variable("GO_TESTENV", ""))
-		build.addDefinition("GO_BUILDENV +=%s", cfg.Variable("GO_BUILDENV", ""))
+		build.addDefinition("GO_BUILDFLAGS :=%s $(GO_BUILDFLAGS)", cfg.Variable("GO_BUILDFLAGS", defaultBuildFlags))
+		build.addDefinition("GO_LDFLAGS :=%s $(GO_LDFLAGS)", cfg.Variable("GO_LDFLAGS", strings.TrimSpace(defaultLdFlags)))
+		build.addDefinition("GO_TESTFLAGS :=%s $(GO_TESTFLAGS)", cfg.Variable("GO_TESTFLAGS", ""))
+		build.addDefinition("GO_TESTENV :=%s $(GO_TESTENV)", cfg.Variable("GO_TESTENV", ""))
+		build.addDefinition("GO_BUILDENV :=%s $(GO_BUILDENV)", cfg.Variable("GO_BUILDENV", ""))
 	}
 	if sr.HasBinInfo {
 		build.addDefinition("")