update to 17

make/compiler_flags

@@ -119,33 +119,9 @@ INC_GTEST ?= -I $(GTEST)/include -I $(GTEST)
 ## setup precompiler options
 CPPFLAGS_BOOST ?= -DBOOST_DISABLE_ASSERTS
 CPPFLAGS_SUNDIALS ?= -DNO_FPRINTF_OUTPUT $(CPPFLAGS_OPTIM_SUNDIALS) $(CXXFLAGS_FLTO_SUNDIALS)
-#CPPFLAGS_GTEST ?=
-STAN_HAS_CXX17 ?= false
-ifeq ($(CXX_TYPE), gcc)
-  GCC_GE_73 := $(shell [ $(CXX_MAJOR) -gt 7 -o \( $(CXX_MAJOR) -eq 7 -a $(CXX_MINOR) -ge 1 \) ] && echo true)
-  ifeq ($(GCC_GE_73),true)
-    STAN_HAS_CXX17 := true
-  endif
-else ifeq ($(CXX_TYPE), clang)
-  CLANG_GE_5 := $(shell [ $(CXX_MAJOR) -gt 5 -o \( $(CXX_MAJOR) -eq 5 -a $(CXX_MINOR) -ge 0 \) ] && echo true)
-  ifeq ($(CLANG_GE_5),true)
-    STAN_HAS_CXX17 := true
-  endif
-else ifeq ($(CXX_TYPE), mingw32-gcc)
-  MINGW_GE_50 := $(shell [ $(CXX_MAJOR) -gt 5 -o \( $(CXX_MAJOR) -eq 5 -a $(CXX_MINOR) -ge 0 \) ] && echo true)
-  ifeq ($(MINGW_GE_50),true)
-    STAN_HAS_CXX17 := true
-  endif
-endif
 
-ifeq ($(STAN_HAS_CXX17), true)
-  CXXFLAGS_LANG ?= -std=c++17
-  CXXFLAGS_STANDARD ?= c++17
-else
-  $(warning "Stan cannot detect if your compiler has the C++17 standard. If it does, please set STAN_HAS_CXX17=true in your make/local file. C++17 support is mandatory in the next release of Stan. Defaulting to C++14")
-  CXXFLAGS_LANG ?= -std=c++1y
-  CXXFLAGS_STANDARD ?= c++1y
-endif
+CXXFLAGS_LANG ?= -std=c++17
+CXXFLAGS_STANDARD ?= c++17
 #CXXFLAGS_BOOST ?=
 CXXFLAGS_SUNDIALS ?= -pipe $(CXXFLAGS_OPTIM_SUNDIALS) $(CPPFLAGS_FLTO_SUNDIALS)
 #CXXFLAGS_GTEST