selftests: alsa: Handle pkg-config failure more gracefully

Follow the pattern used by other selftests like memfd and fall back on the
standard toolchain options to build with a system installed alsa-lib if
we don't get anything from pkg-config. This reduces our build dependencies
a bit in the common case while still allowing use of pkg-config in case
there is a need for it.
Signed-off-by: NMark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220531151337.2933810-1-broonie@kernel.orgSigned-off-by: NTakashi Iwai <tiwai@suse.de>

tools/testing/selftests/alsa/Makefile

@@ -3,6 +3,9 @@
 
 CFLAGS += $(shell pkg-config --cflags alsa)
 LDLIBS += $(shell pkg-config --libs alsa)
+ifeq ($(LDLIBS),)
+LDLIBS += -lasound
+endif
 
 TEST_GEN_PROGS := mixer-test