enable C++17 for gcc

Makefile.linux

@@ -15,13 +15,14 @@ ifeq ($(shell expr match $(CXX) 'clang'),5)
 	NEEDED_CXXFLAGS += -std=c++11
 else ifeq ($(shell expr match ${CXXVER} "4\.[0-9][0-9]"),4) # gcc >= 4.10
 	NEEDED_CXXFLAGS += -std=c++11
-else ifeq ($(shell expr match ${CXXVER} "4\.[7-9]"),3) # >= 4.7
+else ifeq ($(shell expr match ${CXXVER} "4\.[7-9]"),3) # gcc 4.7 - 4.9
 	NEEDED_CXXFLAGS += -std=c++11 -D_GLIBCXX_USE_NANOSLEEP=1
-else ifeq ($(shell expr match ${CXXVER} "4\.6"),3) # = 4.6
+else ifeq ($(shell expr match ${CXXVER} "[5-6]"),1) # gcc 5 - 6
-	NEEDED_CXXFLAGS += -std=c++0x
-else ifeq ($(shell expr match ${CXXVER} "[5-9]"),1) # gcc >= 5
 	NEEDED_CXXFLAGS += -std=c++11
 	LDLIBS = -latomic
+else ifeq ($(shell expr match ${CXXVER} "[7-9]"),1) # gcc >= 7
+	NEEDED_CXXFLAGS += -std=c++17
+	LDLIBS = -latomic
 else # not supported
 $(error Compiler too old)
 endif