[makefile] fix build with g++ 10

Signed-off-by: R4SAS <r4sas@i2pmail.org>

Makefile.linux

@@ -20,7 +20,7 @@ else ifeq ($(shell expr match ${CXXVER} "4\.[7-9]"),3) # gcc 4.7 - 4.9
 else ifeq ($(shell expr match ${CXXVER} "[5-6]"),1) # gcc 5 - 6
 	NEEDED_CXXFLAGS += -std=c++11
 	LDLIBS = -latomic
-else ifeq ($(shell expr match ${CXXVER} "[7-9]"),1) # gcc >= 7
+else ifeq ($(shell expr match ${CXXVER} "[7-9]\|1[0-9]"),2) # gcc >= 7
 	NEEDED_CXXFLAGS += -std=c++17
 	LDLIBS = -latomic
 else # not supported

Makefile.mingw

@@ -2,10 +2,19 @@ USE_WIN32_APP=yes
 CXX = g++
 WINDRES = windres
 CXXFLAGS := ${CXX_DEBUG} -D_MT -DWIN32 -D_WINDOWS -DWIN32_LEAN_AND_MEAN
-NEEDED_CXXFLAGS = -std=c++11
 INCFLAGS = -Idaemon -I.
 LDFLAGS := ${LD_DEBUG} -Wl,-Bstatic -static-libgcc -static-libstdc++
 
+# detect proper flag for c++11 support by compilers
+CXXVER := $(shell $(CXX) -dumpversion)
+ifeq ($(shell expr match ${CXXVER} "[4]\.[7-9]\|4\.1[0-9]\|[5-6]"),4) # gcc 4.7 - 6
+	NEEDED_CXXFLAGS += -std=c++11
+else ifeq ($(shell expr match ${CXXVER} "[7-9]\|1[0-9]"),2) # gcc >= 7
+	NEEDED_CXXFLAGS += -std=c++17
+else # not supported
+$(error Compiler too old)
+endif
+
 # Boost libraries suffix
 BOOST_SUFFIX = -mt