Makefile: support overriding CGO_ENABLED
We generally want CGO_ENABLED=0, but cgo is required for odroid.
This change makes the following work:
make manager CGO_ENABLED=1 GOTAGS=odroid
diff --git a/Makefile b/Makefile
index 6cd7a51..fa9669e 100644
@@ -40,7 +40,8 @@
HOSTGO := go
# By default, build all Go binaries as static. We don't need cgo and it is
# known to cause problems at least on Android emulator.
+CGO_ENABLED ?= 0
TARGETGOOS := $(TARGETOS)
TARGETGOARCH := $(TARGETVMARCH)