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.

Makefile

@@ -24,17 +24,21 @@ GENH_INT = src/internal/version.h
 IMPH = src/internal/stdio_impl.h src/internal/pthread_impl.h src/internal/libc.h
 
 LDFLAGS =
+LDFLAGS_AUTO =
 LIBCC = -lgcc
 CPPFLAGS =
-CFLAGS = -Os -pipe
+CFLAGS =
+CFLAGS_AUTO = -Os -pipe
 CFLAGS_C99FSE = -std=c99 -ffreestanding -nostdinc 
 
 CFLAGS_ALL = $(CFLAGS_C99FSE)
 CFLAGS_ALL += -D_XOPEN_SOURCE=700 -I./arch/$(ARCH) -I./src/internal -I./include
-CFLAGS_ALL += $(CPPFLAGS) $(CFLAGS)
+CFLAGS_ALL += $(CPPFLAGS) $(CFLAGS_AUTO) $(CFLAGS)
 CFLAGS_ALL_STATIC = $(CFLAGS_ALL)
 CFLAGS_ALL_SHARED = $(CFLAGS_ALL) -fPIC -DSHARED
 
+LDFLAGS_ALL = $(LDFLAGS_AUTO) $(LDFLAGS)
+
 AR      = $(CROSS_COMPILE)ar
 RANLIB  = $(CROSS_COMPILE)ranlib
 INSTALL = ./tools/install.sh
@@ -146,7 +150,7 @@ endif
 	$(CC) $(CFLAGS_ALL_SHARED) -c -o $@ $<
 
 lib/libc.so: $(LOBJS)
-	$(CC) $(CFLAGS_ALL_SHARED) $(LDFLAGS) -nostdlib -shared \
+	$(CC) $(CFLAGS_ALL_SHARED) $(LDFLAGS_ALL) -nostdlib -shared \
 	-Wl,-e,_dlstart -Wl,-Bsymbolic-functions \
 	-o $@ $(LOBJS) $(LIBCC)
 

configure

@@ -629,12 +629,14 @@ libdir = $libdir
 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