[REVERT ME] libvisual-plugins: Drop troublesome "--install" from ACLOCAL_AMFLAGS

.. and remake installation of file m4/alsa.m4 .

This reverts commit 9b420cc.

Author: hartwork

libvisual-plugins/Makefile.am

@@ -1,6 +1,6 @@
 ## Process this file with automake to generate a Makefile.in
 
-ACLOCAL_AMFLAGS = -I m4 --install
+ACLOCAL_AMFLAGS = -I m4
 
 SUBDIRS = plugins po
 

libvisual-plugins/autogen.sh

@@ -4,9 +4,23 @@
 
 set -e -u
 
+mkdir -p m4/
+
 if [[ "$(uname -s)" == Darwin ]]; then
-    # This provides a dummy substitute to alsa.m4 on macOS
-    echo 'AC_DEFUN([AM_PATH_ALSA], [HAVE_ALSA=no])' > acinclude.m4
+    # This provides a dummy substitute to alsa.m4 on macOS.. and is a reason
+    # why "make dist" should be run on Linux rather than on macOS.
+    echo 'AC_DEFUN([AM_PATH_ALSA], [HAVE_ALSA=no])' > m4/alsa.m4
+else
+    # This will make aclocal add line "m4_include([m4/alsa.m4])"
+    # to file acinclude.m4 rather than inlining that file's content.
+    # As a result, packagers are able to run ./autogen.sh (or autoreconf)
+    # with no ALSA development files installed.
+    alsa_m4="$(aclocal --print-ac-dir)"/alsa.m4
+    if [[ -f "${alsa_m4}" ]]; then
+        cp -v "${alsa_m4}" m4/alsa.m4
+    else
+        rm -f -v m4/alsa.m4
+    fi
 fi
 
 autoreconf --install --verbose --force || \