After typing "./configure":

checking build system type... x86_64-apple-darwin18.6.0
checking ARCH... mac686
checking setting AR... ... ar
checking setting ARFLAGS... ... ruv
checking whether the Fortran compiler works... yes
checking for Fortran compiler default output file name... a.out
checking for suffix of executables...
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU Fortran compiler... yes
checking whether /usr/local/bin/gfortran accepts -g... yes
checking for gcc... /usr/local/bin/gcc
checking whether we are using the GNU C compiler... yes
checking whether /usr/local/bin/gcc accepts -g... yes
checking for /usr/local/bin/gcc option to accept ISO C89... unsupported
checking for mpif90... no
checking for ifort... no
checking for gfortran... gfortran
checking whether we are using the GNU Fortran compiler... yes
checking whether gfortran accepts -g... yes
checking version of gfortran... gfortran 7.1
checking for Fortran flag to compile .f90 files... none
setting F90... gfortran
setting MPIF90... gfortran
checking whether we are using the GNU C compiler... (cached) yes
checking whether /usr/local/bin/gcc accepts -g... (cached) yes
checking for /usr/local/bin/gcc option to accept ISO C89... (cached) unsupported
setting CC... /usr/local/bin/gcc
setting CFLAGS... -O3
checking whether we are using the GNU Fortran 77 compiler... yes
checking whether /usr/local/bin/gfortran accepts -g... yes
setting F77... /usr/local/bin/gfortran
using F90... gfortran
setting FFLAGS... -O3 -g
setting F90FLAGS... $(FFLAGS) -x f95-cpp-input
setting FFLAGS_NOOPT... -O0 -g
setting CPP... cpp
setting CPPFLAGS... -P -traditional
setting LD... gfortran
setting LDFLAGS... -g
checking whether make sets $(MAKE)... yes
checking whether Fortran files must be preprocessed... no
checking for library containing dgemm... no
MKL not found
in /opt/intel/mkl/lib:  checking for library containing dgemm... no
MKL not found
checking for library containing dgemm... no
in /usr/local/lib:  checking for library containing dgemm... no
checking for library containing dgemm... -lblas
setting BLAS_LIBS... -lblas
checking for library containing dspev... -llapack
checking how to run the C preprocessor... /lib/cpp
configure: error: in `/Users/johnschneeloch/Documents/espresso/qe-6.4.1':
configure: error: C preprocessor "/lib/cpp" fails sanity check
See `config.log' for more details