In case you see that Spack reports an error in which points to a non-spack directory, maybe you are forcing your compiler to look at places it shouldn’t. Please avoid setting environment variables such as CPLUS_INCLUDE_PATH, LD_LIBRARY_PATH, or LIBRARY_PATH when using Spack. This can particularly lead to problems if you have a (broken) installation of a requested dependency in that path.
Keep in mind that, by default, Spack will use the default compiler of your system.