Currently in QuickFIX-1.13.3, the UnitTest++ Makefile is hardcoded to use
CXX = g++
It would help if that were instead
CXX ?= g++
so that UnitTest++ will build with the same compiler that QuickFIX does. This is important because some operating systems have more than one compiler which use incompatible CFLAGS. Inheriting the CFLAGS but not inheriting CXX can cause an error.