Allow user-specified CFLAGS and LDFLAGS via USER_CFLAGS and USER_LDFLAGS.

=== modified file 'spim/Makefile'
--- spim/Makefile	2008-11-11 23:13:07 +0000
+++ spim/Makefile	2008-11-11 23:21:19 +0000
@@ -93,10 +93,10 @@
 DEFINES = $(ENDIAN) $(MEM_SIZES) -DDEFAULT_EXCEPTION_HANDLER="\"$(EXCEPTION_DIR)/exceptions.s\"" -DSPIM_VERSION="\"`cat ../VERSION`\""
 
 CC = gcc
-CFLAGS = -I. -I$(CPU_DIR) $(DEFINES) -g -Wall
+CFLAGS = -I. -I$(CPU_DIR) $(DEFINES) -Wall $(USER_CFLAGS)
 YFLAGS = -d --file-prefix=y
 YCFLAGS =
-LDFLAGS = -lm
+LDFLAGS = -lm $(USER_LDFLAGS)
 CSH = bash
 
 # lex.yy.c is usually compiled with -O to speed it up.