keep user-provided CFLAGS/LDFLAGS separate from those added by configure
this way, overriding these variables on the make command line (or just
re-passing the originally-passed values when invoking make) won't
suppress use of the flags added by configure.
diff --git a/configure b/configure
index 742ca26..3e536f5 100755
--- a/configure
+++ b/configure
@@ -629,12 +629,14 @@
includedir = $includedir
syslibdir = $syslibdir
CC = $CC
-CFLAGS = $CFLAGS_AUTO $CFLAGS
+CFLAGS = $CFLAGS
+CFLAGS_AUTO = $CFLAGS_AUTO
CFLAGS_C99FSE = $CFLAGS_C99FSE
CFLAGS_MEMOPS = $CFLAGS_MEMOPS
CFLAGS_NOSSP = $CFLAGS_NOSSP
CPPFLAGS = $CPPFLAGS
-LDFLAGS = $LDFLAGS_AUTO $LDFLAGS
+LDFLAGS = $LDFLAGS
+LDFLAGS_AUTO = $LDFLAGS_AUTO
CROSS_COMPILE = $CROSS_COMPILE
LIBCC = $LIBCC
OPTIMIZE_GLOBS = $OPTIMIZE_GLOBS