Use CFLAGS from environment and make sure we install the .m4 into the
correct place regardless of whether `aclocal` is installed on the host.

--- configure
+++ configure
@@ -21459,8 +21459,9 @@
     ;;
 esac
 
-CFLAGS="-O3 -Wall -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE $CFLAGS"
-DEBUG_CFLAGS="-g -DDEBUG $CFLAGS"
+CFLAGS="$CFLAGS -Wall"
+CPPFLAGS="$CPPFLAGS -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE"
+DEBUG_CFLAGS="$CFLAGS -g -DDEBUG"
 
 
 
--- m4/Makefile.in
+++ m4/Makefile.in
@@ -116,8 +116,7 @@
 
 EXTRA_DIST = dvdnav.m4
 
-@INSTALL_M4_TRUE@m4datadir = @ACLOCAL_DIR@
-@INSTALL_M4_FALSE@m4datadir = $(datadir)/aclocal
+m4datadir = $(datadir)/aclocal
 
 m4data_DATA = dvdnav.m4
 subdir = m4