Allow building libsigrok without libserialport.
Since the DER EE DE-5000 driver is currently the only user of
the es51919 module and it depends on the libserialport, compile
the module only if the DER EE DE-5000 driver is enabled. This
allows libsigrok to be built without libserialport again.
diff --git a/Makefile.am b/Makefile.am
index ca70c4d..10c0400 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -107,8 +107,10 @@
src/dmm/bm25x.c
# Hardware (LCR chip parsers)
+if HW_DEREE_DE5000
libsigrok_la_SOURCES += \
src/lcr/es51919.c
+endif
# Hardware drivers
if HW_AGILENT_DMM