Allow setting binarypath from Makefile

Packagers for other distributions and package managers may put their helper binaries in other location prefixes.
Add HELPER_BINARIES_DIR to the makefile so packagers can set the prefix when building Podman.
HELPER_BINARIES_DIR will be set at link-time.

Example usage: make podman-remote HELPER_BINARIES_DIR=/my/location/prefix

Signed-off-by: Ashley Cui <acui@redhat.com>

Makefile

@@ -102,6 +102,7 @@ LDFLAGS_PODMAN ?= \
 	-X $(LIBPOD)/define.buildInfo=$(BUILD_INFO) \
 	-X $(LIBPOD)/config._installPrefix=$(PREFIX) \
 	-X $(LIBPOD)/config._etcDir=$(ETCDIR) \
+	-X github.com/containers/common/pkg/config.additionalHelperBinariesDir=$(HELPER_BINARIES_DIR)\
 	$(EXTRA_LDFLAGS)
 LDFLAGS_PODMAN_STATIC ?= \
 	$(LDFLAGS_PODMAN) \