change override -std=c++14 to append

Author: yingyue2030699

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
       - name: Build tests with coverage
         run: |
           make clean
-          make test COVERAGE=1 CXX=g++ CXXFLAGS="-std=c++14 -O0 -g --coverage" LDFLAGS="--coverage"
+          make test COVERAGE=1 CXX=g++ CXXFLAGS="-O0 -g --coverage" LDFLAGS="--coverage"
 
       - name: Run tests
         run: ./bin/test_main

Makefile

@@ -141,7 +141,7 @@ INTEL  = $(shell type icpc  >/dev/null 2>&1; echo $$?)
 GCC    = $(shell type g++   >/dev/null 2>&1; echo $$?)
 
 INCS    = $(shell gsl-config --cflags) -Iinclude -Iinclude/*
-CXXFLAGS = -std=c++14
+CXXFLAGS += -std=c++14
 LIBS     = $(shell gsl-config --libs)
 
 # Add pthread to library if multithreading (embarrassingly parallel) is needed