alsa: Fix mixer path when running from build tree

The mixer paths are not available in ${builddir} - we need to look in
${srcdir}. This should fix running an in-tree build without make install
as well as alsa-mixer-path-test in make distcheck.

Since the most straightforward way to define PA_SRCDIR was in
Makefile.am, I'm moving PA_BUILDDIR there as well for consistency.

src/Makefile.am

@@ -48,7 +48,9 @@ AM_CPPFLAGS = \
 	-DPA_ALSA_PATHS_DIR=\"$(alsapathsdir)\" \
 	-DPA_ALSA_PROFILE_SETS_DIR=\"$(alsaprofilesetsdir)\"
 AM_CFLAGS = \
-	$(PTHREAD_CFLAGS)
+	$(PTHREAD_CFLAGS) \
+	-DPA_SRCDIR=\"$(abs_srcdir)\" \
+	-DPA_BUILDDIR=\"$(abs_builddir)\"
 AM_CXXFLAGS = $(AM_CFLAGS)
 SERVER_CFLAGS = -D__INCLUDED_FROM_PULSE_AUDIO
 

src/modules/alsa/alsa-mixer.c

@@ -2373,7 +2373,7 @@ static int path_verify(pa_alsa_path *p) {
 
 static const char *get_default_paths_dir(void) {
     if (pa_run_from_build_tree())
-        return PA_BUILDDIR "/modules/alsa/mixer/paths/";
+        return PA_SRCDIR "/modules/alsa/mixer/paths/";
     else
         return PA_ALSA_PATHS_DIR;
 }

src/tests/alsa-mixer-path-test.c

@@ -16,7 +16,7 @@
 /* This function was copied from alsa-mixer.c */
 static const char *get_default_paths_dir(void) {
     if (pa_run_from_build_tree())
-        return PA_BUILDDIR "/modules/alsa/mixer/paths/";
+        return PA_SRCDIR "/modules/alsa/mixer/paths/";
     else
         return PA_ALSA_PATHS_DIR;
 }