build: use AX_IS_RELEASE() and AX_COMPILER_FLAGS()

The autoconf macros AX_COMPILER_FLAGS_{CFLAGS|GIR|LDFLAGS} test
for compiler and linker support of various flags, and add the flags to
the generated output.

If the command-line option '--enable-compile-warnings' is specified to
'configure', a number of additional warning options is also added to the
output. This is the default.

This update requires the presence of the GNU autoconf-archive in the
system.

libqcdm/src/Makefile.am

@@ -1,5 +1,13 @@
-AM_CFLAGS = $(CODE_COVERAGE_CFLAGS)
-AM_LDFLAGS = $(CODE_COVERAGE_LDFLAGS)
+
+AM_CFLAGS = \
+	$(WARN_CFLAGS) \
+	$(CODE_COVERAGE_CFLAGS) \
+	$(NULL)
+
+AM_LDFLAGS = \
+	$(WARN_LDFLAGS) \
+	$(CODE_COVERAGE_LDFLAGS) \
+	$(NULL)
 
 noinst_LTLIBRARIES = libqcdm.la libqcdm-test.la
 
@@ -41,4 +49,3 @@ libqcdm_test_la_SOURCES = \
 
 libqcdm_test_la_LIBADD = \
 	$(MM_LIBS)
-

libqcdm/tests/Makefile.am

@@ -1,7 +1,14 @@
 include $(top_srcdir)/gtester.make
 
-AM_CFLAGS = $(CODE_COVERAGE_CFLAGS)
-AM_LDFLAGS = $(CODE_COVERAGE_LDFLAGS)
+AM_CFLAGS = \
+	$(WARN_CFLAGS) \
+	$(CODE_COVERAGE_CFLAGS) \
+	$(NULL)
+
+AM_LDFLAGS = \
+	$(WARN_LDFLAGS) \
+	$(CODE_COVERAGE_LDFLAGS) \
+	$(NULL)
 
 noinst_PROGRAMS = test-qcdm modepref ipv6pref reset
 TEST_PROGS += test-qcdm