Build: Autotools usage improvements

Use libtool defaults.
Define CXXFLAGS rather than CFLAGS.
Add libraries via LIBADD rather than LDFLAGS.  This allows
  --as-needed to drop unnecessary libs if present.
Don't bother with PIC objects for convenience library.

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Change-Id: I4a6079402a01ad5f6ccfb71ca9fca44c567ec62d
diff --git a/Makefile.am b/Makefile.am
index ee6e7a8..7bfb12a 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,16 +1,17 @@
 sbin_PROGRAMS = phosphor-hwmon-readd
 
 phosphor_hwmon_readd_SOURCES = readd.cpp
-phosphor_hwmon_readd_LDADD = libhwmon.la
-phosphor_hwmon_readd_LDFLAGS = $(SDBUSPLUS_LIBS)
-phosphor_hwmon_readd_CFLAGS = $(SDBUSPLUS_CFLAGS)
+phosphor_hwmon_readd_LDADD = $(SDBUSPLUS_LIBS) libhwmon.la
+phosphor_hwmon_readd_CXXFLAGS = $(SDBUSPLUS_CFLAGS)
 
 noinst_LTLIBRARIES = libhwmon.la
-libhwmon_la_LDFLAGS = \
+libhwmon_la_LDFLAGS = -static
+libhwmon_la_LIBADD = \
 	$(SDBUSPLUS_LIBS) \
 	$(PHOSPHOR_DBUS_INTERFACES_LIBS) \
 	$(PHOSPHOR_LOGGING_LIBS)
-libhwmon_la_CFLAGS = $(SDBUSPLUS_CFLAGS) \
+libhwmon_la_CXXFLAGS = \
+	$(SDBUSPLUS_CFLAGS) \
 	$(PHOSPHOR_DBUS_INTERFACES_CFLAGS) \
 	$(PHOSPHOR_LOGGING_CFLAGS)