SRCS must be set using := or things break when ASM_OBJS is added to OBJS

Originally committed as revision 5069 to svn://svn.ffmpeg.org/ffmpeg/trunk

common.mak

@@ -19,7 +19,7 @@ ifeq ($(TARGET_ARCH_SPARC64),yes)
 CFLAGS+= -mcpu=ultrasparc -mtune=ultrasparc
 endif
 
-SRCS = $(OBJS:.o=.c) $(ASM_OBJS:.o=.S) $(CPPOBJS:.o=.cpp)
+SRCS := $(OBJS:.o=.c) $(ASM_OBJS:.o=.S) $(CPPOBJS:.o=.cpp)
 OBJS := $(OBJS) $(ASM_OBJS) $(CPPOBJS)
 STATIC_OBJS := $(OBJS) $(STATIC_OBJS)
 SHARED_OBJS := $(OBJS) $(SHARED_OBJS)