add gcc 9 support

Makefile.linux

@@ -19,10 +19,7 @@ else ifeq ($(shell expr match ${CXXVER} "4\.[7-9]"),3) # >= 4.7
 	NEEDED_CXXFLAGS += -std=c++11 -D_GLIBCXX_USE_NANOSLEEP=1
 else ifeq ($(shell expr match ${CXXVER} "4\.6"),3) # = 4.6
 	NEEDED_CXXFLAGS += -std=c++0x
-else ifeq ($(shell expr match ${CXXVER} "[5-7]\.[0-9]"),3) # gcc >= 5.0
-	NEEDED_CXXFLAGS += -std=c++11
-	LDLIBS = -latomic
-else ifeq ($(shell expr match ${CXXVER} "[7-8]"),1) # gcc 7 ubuntu or gcc 8 arch
+else ifeq ($(shell expr match ${CXXVER} "[5-9]"),1) # gcc >= 5
 	NEEDED_CXXFLAGS += -std=c++11
 	LDLIBS = -latomic
 else # not supported