libevl: fix the compile failed caused by the Wshadow flag

Libevl use *-Wshadow=local* flags in config.mk. However this flag is
only valid when version >=7, otherwise gcc will complain :
"unrecognized command line option ‘-Wshadow=local’; did you mean
‘-Wshadow-ivar’?"
and compile will be failed.

This patch fix this probelm.
Signed-off-by: lio <liu.hailong6@zte.com.cn>
Signed-off-by: Philippe Gerum <rpm@xenomai.org>

config.mk

@@ -61,12 +61,19 @@ endif
 
 BASE_CPPFLAGS := -D_GNU_SOURCE -D_REENTRANT $(DEBUG_CPPFLAGS)
 
+GCCVER_GTE_7 := $(shell expr `${CC} -dumpversion | cut -f1 -d.` \>= 7)
+ifeq "$(GCCVER_GTE_7)" "1"
+	WSHADOW_FLAG="-Wshadow=local"
+else
+	WSHADOW_FLAG=
+endif
+
 BASE_CFLAGS :=	-pipe -fstrict-aliasing	 					\
 		-Wall -Wstrict-prototypes -Wmissing-prototypes -Wno-long-long	\
-		-Wno-unused-parameter -Wshadow=local -Werror $(DEBUG_CFLAGS)
+		-Wno-unused-parameter ${WSHADOW_FLAG} -Werror $(DEBUG_CFLAGS)
 
 BASE_CXXFLAGS := -pipe -fstrict-aliasing -Wall -Wno-long-long	\
-		-Wno-unused-parameter -Wshadow=local -Werror $(DEBUG_CFLAGS)
+		-Wno-unused-parameter ${WSHADOW_FLAG} -Werror $(DEBUG_CFLAGS)
 
 # Easy way to hide commas in args from $(call ...) invocations
 comma := ,