add make target to build static binary

This is useful to generate a binary that can be dropped
onto any arbitrary distro, such as CoreOS, without having
to worry about glibc or other dependencies.

Specifically: CoreOS uses glibc, but it does not have a
package manager. It also has a read-only OS (`/usr/`).
Thus I'd like to compile a binary that can be dropped
into CoreOS and have zero dependencies.

* `make build` builds the same as it did before this commit.
* `make all` builds both dynamic and static bins, as expected.

I struggled with a way to DRY this up _and_ avoid diff churn.
In the end, I went with simplicity even though it's not DRY.

.gitignore

@@ -6,4 +6,5 @@ old/
 tmp/
 *_stringer.go
 mgmt
+mgmt.static
 rpmbuild/

Makefile

@@ -38,7 +38,7 @@ USERNAME := $(shell cat ~/.config/copr 2>/dev/null | grep username | awk -F '='
 SERVER = 'dl.fedoraproject.org'
 REMOTE_PATH = 'pub/alt/$(USERNAME)/$(PROGRAM)'
 
-all: docs
+all: docs $(PROGRAM).static
 
 # show the current version
 version:
@@ -72,6 +72,16 @@ else
 	go build -ldflags "-X main.program=$(PROGRAM) -X main.version=$(SVERSION)" -o $(PROGRAM);
 endif
 
+$(PROGRAM).static: main.go
+	@echo "Building: $(PROGRAM).static, version: $(SVERSION)..."
+	go generate
+ifneq ($(OLDGOLANG),)
+	@# avoid equals sign in old golang versions eg in: -X foo=bar
+	go build -a -installsuffix cgo -tags netgo -ldflags '-extldflags "-static" -X main.program $(PROGRAM) -X main.version $(SVERSION)' -o $(PROGRAM).static;
+else
+	go build -a -installsuffix cgo -tags netgo -ldflags '-extldflags "-static" -X main.program=$(PROGRAM) -X main.version=$(SVERSION)' -o $(PROGRAM).static;
+endif
+
 clean:
 	[ ! -e $(PROGRAM) ] || rm $(PROGRAM)
 	rm -f *_stringer.go	# generated by `go generate`