unix/Makefile: Remove explicit addition of -std=c++ flag.

This was added merely for building the C++ user module example, so it's a
better fit to add it in the corresponding micropython.mk.

examples/usercmodule/cppexample/micropython.mk

@@ -6,7 +6,7 @@ SRC_USERMOD_CXX += $(CPPEXAMPLE_MOD_DIR)/example.cpp
 
 # Add our module directory to the include path.
 CFLAGS_USERMOD += -I$(CPPEXAMPLE_MOD_DIR)
-CXXFLAGS_USERMOD += -I$(CPPEXAMPLE_MOD_DIR)
+CXXFLAGS_USERMOD += -I$(CPPEXAMPLE_MOD_DIR) -std=c++11
 
 # We use C++ features so have to link against the standard library.
 LDFLAGS_USERMOD += -lstdc++

ports/unix/Makefile

@@ -270,12 +270,6 @@ CFLAGS += -DMPZ_DIG_SIZE=16 # force 16 bits to work on both 32 and 64 bit archs
 CFLAGS += -DMICROPY_MODULE_FROZEN_STR
 endif
 
-HASCPP17 = $(shell expr `$(CC) -dumpversion | cut -f1 -d.` \>= 7)
-ifeq ($(HASCPP17), 1)
-	CXXFLAGS += -std=c++17
-else
-	CXXFLAGS += -std=c++11
-endif
 CXXFLAGS += $(filter-out -Wmissing-prototypes -Wold-style-definition -std=gnu99,$(CFLAGS) $(CXXFLAGS_MOD))
 
 ifeq ($(MICROPY_FORCE_32BIT),1)