Use CFLAGS from environment and make sure we install the .m4 into the
correct place regardless of whether `aclocal` is installed on the host.
Index: libdvdnav-0.1.10/configure.ac
===================================================================
--- libdvdnav-0.1.10.orig/configure.ac
+++ libdvdnav-0.1.10/configure.ac
@@ -175,8 +175,9 @@ dnl ------------------------------------
 dnl cflags
 dnl ---------------------------------------------
 dnl Common cflags for all platforms
-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"
 
 AC_SUBST(DEBUG_CFLAGS)
 
Index: libdvdnav-0.1.10/m4/Makefile.am
===================================================================
--- libdvdnav-0.1.10.orig/m4/Makefile.am
+++ libdvdnav-0.1.10/m4/Makefile.am
@@ -2,10 +2,6 @@ include $(top_srcdir)/misc/Makefile.comm
 
 EXTRA_DIST = dvdnav.m4
 
-if INSTALL_M4
-m4datadir = @ACLOCAL_DIR@
-else
 m4datadir = $(datadir)/aclocal
-endif
 
 m4data_DATA = dvdnav.m4