Add BOOST_MATH_STANDALONE flag

Author: andrjohns

make/compiler_flags

@@ -127,7 +127,7 @@ INC_SUNDIALS ?= $(INC_DIR_OPT) $(SUNDIALS)/include $(INC_DIR_OPT) $(SUNDIALS)/sr
 INC_GTEST ?= $(INC_DIR_OPT) $(GTEST)/include $(INC_DIR_OPT) $(GTEST)
 
 ## setup precompiler options
-CPPFLAGS_BOOST ?= -DBOOST_DISABLE_ASSERTS
+CPPFLAGS_BOOST ?= -DBOOST_DISABLE_ASSERTS -DBOOST_MATH_STANDALONE
 CPPFLAGS_SUNDIALS ?= -DNO_FPRINTF_OUTPUT $(CPPFLAGS_OPTIM_SUNDIALS) $(CXXFLAGS_FLTO_SUNDIALS)
 
 CXXFLAGS_LANG ?= -std=c++17