Comment (by Roland Haas):

Removing CXXFLAGS and CPPFLAGS from the LD line leads to link time failures about GOMP_parallel not being found. Adding LD_OPENMP_FLAGS = -fopenmp does not help since that variable is not used. The only X_OPENMP_FLAGS variables in configure are:

lib/make/configure:F77_OPENMP_FLAGS="$F90_OPENMP_FLAGS"
lib/make/configure:s%@CPP_OPENMP_FLAGS@%$CPP_OPENMP_FLAGS%g
lib/make/configure:s%@FPP_OPENMP_FLAGS@%$FPP_OPENMP_FLAGS%g
lib/make/configure:s%@C_OPENMP_FLAGS@%$C_OPENMP_FLAGS%g
lib/make/configure:s%@CXX_OPENMP_FLAGS@%$CXX_OPENMP_FLAGS%g
lib/make/configure:s%@CUCC_OPENMP_FLAGS@%$CUCC_OPENMP_FLAGS%g
lib/make/configure:s%@F90_OPENMP_FLAGS@%$F90_OPENMP_FLAGS%g
lib/make/configure:s%@F77_OPENMP_FLAGS@%$F77_OPENMP_FLAGS%g

So one first needs to define a new variable LD_OPENMP_FLAGS then make sure it gets added to LDFLAGS and then one can remove CXXFLAGS. Probably also a good idea to set LD_OPENMP_FLAGS to the same default as CXX_OPENMP_FLAGS in lib/make/known-architectures/linux

If one wants to preserve backwards compatibility then one also needs to default LD_OPENMP_FLAGS to CXX_OPENMP_FLAGS.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2553/cactus-link-command-uses-cppflags-and