compiling PETSc produces warnings

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Configuring PETSc to compile on your system
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***** WARNING: CC (set to gcc) found in environment variables - ignoring
use ./configure CC=$CC if you really want to use that value ******
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***** WARNING: CFLAGS (set to -g -std=gnu99 -O2 -fopenmp -Wall) found in environment variables - i
use ./configure CFLAGS=$CFLAGS if you really want to use that value ******
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***** WARNING: CXX (set to g++) found in environment variables - ignoring
use ./configure CXX=$CXX if you really want to use that value ******
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***** WARNING: CXXFLAGS (set to -g -std=gnu++14 -O2 -fopenmp -Wall) found in environment variables
use ./configure CXXFLAGS=$CXXFLAGS if you really want to use that value ******
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***** WARNING: F77 (set to gfortran) found in environment variables - ignoring
use ./configure F77=$F77 if you really want to use that value ******
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***** WARNING: F90 (set to gfortran) found in environment variables - ignoring
use ./configure F90=$F90 if you really want to use that value ******
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***** WARNING: F90FLAGS (set to -g -fcray-pointer -ffixed-line-length-none -O2 -fopenmp -Wall) fou
use ./configure F90FLAGS=$F90FLAGS if you really want to use that value ******
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***** WARNING: CPP (set to cpp) found in environment variables - ignoring
use ./configure CPP=$CPP if you really want to use that value ******
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***** WARNING: CPPFLAGS (set to
-fopenmp -Wall) found in environment variables - ignoring
use ./configure CPPFLAGS=$CPPFLAGS if you really want to use that value ******
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***** WARNING: LDFLAGS (set to -rdynamic) found in environment variables - ignoring
use ./configure LDFLAGS=$LDFLAGS if you really want to use that value ******
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***** WARNING: MPI_DIR (set to /usr) found in environment variables - ignoring
use ./configure MPI_DIR=$MPI_DIR if you really want to use that value ******
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***** WARNING: MAKEFLAGS (set to w -- CCTK_TARGET=make.checked CCTK_HOME=/data/rhaas/postdoc/gr/ca
use ./configure MAKEFLAGS=$MAKEFLAGS if you really want to use that value ******
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***** WARNING: AR (set to ar) found in environment variables - ignoring
use ./configure AR=$AR if you really want to use that value ******
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