fix CC assignment in Makefiles of answers

labcodes_answer/lab3_result/Makefile

@@ -47,7 +47,7 @@ HOSTCFLAGS	:= -g -Wall -O2
 
 GDB		:= $(GCCPREFIX)gdb
 
-CC		?= $(GCCPREFIX)gcc
+CC		:= $(GCCPREFIX)gcc
 CFLAGS	:= -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc $(DEFS)
 CFLAGS	+= $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 CTYPE	:= c S

labcodes_answer/lab4_result/Makefile

@@ -47,7 +47,7 @@ HOSTCFLAGS	:= -g -Wall -O2
 
 GDB		:= $(GCCPREFIX)gdb
 
-CC		?= $(GCCPREFIX)gcc
+CC		:= $(GCCPREFIX)gcc
 CFLAGS	:= -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc $(DEFS)
 CFLAGS	+= $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 CTYPE	:= c S

labcodes_answer/lab5_result/Makefile

@@ -47,7 +47,7 @@ HOSTCFLAGS	:= -g -Wall -O2
 
 GDB		:= $(GCCPREFIX)gdb
 
-CC		?= $(GCCPREFIX)gcc
+CC		:= $(GCCPREFIX)gcc
 CFLAGS	:= -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc $(DEFS)
 CFLAGS	+= $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 CTYPE	:= c S

labcodes_answer/lab6_result/Makefile

@@ -47,7 +47,7 @@ HOSTCFLAGS	:= -g -Wall -O2
 
 GDB		:= $(GCCPREFIX)gdb
 
-CC		?= $(GCCPREFIX)gcc
+CC		:= $(GCCPREFIX)gcc
 CFLAGS	:= -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc $(DEFS)
 CFLAGS	+= $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 CTYPE	:= c S

labcodes_answer/lab7_result/Makefile

@@ -47,7 +47,7 @@ HOSTCFLAGS	:= -g -Wall -O2
 
 GDB		:= $(GCCPREFIX)gdb
 
-CC		?= $(GCCPREFIX)gcc
+CC		:= $(GCCPREFIX)gcc
 CFLAGS	:= -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc $(DEFS)
 CFLAGS	+= $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 CTYPE	:= c S

labcodes_answer/lab8_result/Makefile

@@ -47,7 +47,7 @@ HOSTCFLAGS	:= -g -Wall -O2 -D_FILE_OFFSET_BITS=64
 
 GDB		:= $(GCCPREFIX)gdb
 
-CC		?= $(GCCPREFIX)gcc
+CC		:= $(GCCPREFIX)gcc
 CFLAGS	:= -fno-builtin -Wall -ggdb -m32 -gstabs -nostdinc $(DEFS)
 CFLAGS	+= $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 CTYPE	:= c S