Vars in Makefile.nek are defined with :=, not =

Makefile.nek.in

 # == Source and destination directories ============================================================
-VPATH    = @srcdir@/Nek5000/core:@srcdir@/Nek5000/core/cmt:@srcdir@/Nek5000/core/3rd_party:@srcdir@/Nek5000/jl
-srcdir   = @srcdir@
-builddir = @builddir@
-objdir   = @builddir@/obj
-includedir = @builddir@/include
+VPATH    := @srcdir@/Nek5000/core:@srcdir@/Nek5000/core/cmt:@srcdir@/Nek5000/core/3rd_party:@srcdir@/Nek5000/jl
+srcdir   := @srcdir@
+builddir := @builddir@
+objdir   := @builddir@/obj
+includedir := @builddir@/include
 
 # == Standard GNU Compilers and flags ==============================================================
-CC       = @CC@
-CFLAGS   = @CFLAGS@
-CPPFLAGS = @CPPFLAGS@ @DEFS@ \
+CC       := @CC@
+CFLAGS   := @CFLAGS@
+CPPFLAGS := @CPPFLAGS@ @DEFS@ \
            -I$(builddir) -I$(includedir) -I$(srcdir)/Nek5000/core -I$(srcdir)/Nek5000/core/cmt \
            -I$(srcdir)/Nek5000/core/3rd_party -I$(srcdir)/Nek5000/jl
-LDFLAGS  = @LDFLAGS@
-LIBS     = @LIBS@
+LDFLAGS  := @LDFLAGS@
+LIBS     := @LIBS@
 
-F77      = @F77@
-FFLAGS   = @FFLAGS@ @FCFLAGS_f@ $(subst -D, @FC_DEFINE@, @DEFS@) \
+F77      := @F77@
+FFLAGS   := @FFLAGS@ @FCFLAGS_f@ $(subst -D, @FC_DEFINE@, @DEFS@) \
            -I$(builddir) -I$(includedir) -I$(srcdir)/Nek5000/core -I$(srcdir)/Nek5000/core/cmt \
            -I$(srcdir)/Nek5000/core/3rd_party -I$(srcdir)/Nek5000/jl
-FLIBS    = @FLIBS@
+FLIBS    := @FLIBS@
 
 # == Nek-only compilers and flags ==================================================================
-nek_debug_flags = @nek_debug_flags@
-nek_opt_flags   = @nek_opt_flags@
-nek_real8_flags = @nek_real8_flags@
-jl_prefix       = @jl_prefix@
+nek_debug_flags := @nek_debug_flags@
+nek_opt_flags   := @nek_opt_flags@
+nek_real8_flags := @nek_real8_flags@
+jl_prefix       := @jl_prefix@
 
 # == FORTRAN objects ===============================================================================
-nek_drive_obj  = $(addprefix $(objdir)/, drive.o)
-
-nek_core_f_obj = $(addprefix $(objdir)/, \
-                 drive1.o drive2.o plan4.o bdry.o coef.o conduct.o connect1.o connect2.o \
-                 dssum.o edgec.o eigsolv.o gauss.o genxyz.o navier1.o makeq.o navier0.o \
-                 navier2.o navier3.o navier4.o prepost.o speclib.o map2.o turb.o mvmesh.o ic.o \
-                 ssolv.o planx.o mxm_wrapper.o hmholtz.o gfdm_par.o  gfdm_op.o gfdm_solve.o \
-                 subs1.o subs2.o genbox.o gmres.o hsmg.o convect.o induct.o perturb.o navier5.o \
-                 navier6.o navier7.o navier8.o fast3d.o fasts.o calcz.o byte_mpi.o postpro.o \
-                 cvode_driver.o vprops.o qthermal.o cvode_aux.o makeq_aux.o papi.o nek_in_situ.o \
-                 readat_new.o @CASENAME@.o)
-
-nek_math_obj   = $(addprefix $(objdir)/, math.o)
-nek_blas_obj   = $(addprefix $(objdir)/, @nek_blas_obj@)   # blas.o | null
-nek_cmt_obj    = $(addprefix $(objdir)/, @nek_cmt_obj@)    # drive1_cmt.o ... | cmt_dummy.o
-nek_lapack_obj = $(addprefix $(objdir)/, @nek_lapack_obj@) # dsygv.o ssygv.o | null
-nek_mpi_obj    = $(addprefix $(objdir)/, @nek_mpi_obj@)    # byte_mpi.o comm_mpi.o | byte_mpi.o comm_mpi.o mpi_dummy.o
-nek_mxm_obj    = $(addprefix $(objdir)/, @nek_mxm_obj@)    # mxm_std.o | mxm_std.o mxm_bgq.o
-nek_neknek_obj = $(addprefix $(objdir)/, @nek_neknek_obj@) # singlmesh.o | multimesh.o
-
-nek_flib_obj   = $(nek_core_f_obj) $(nek_math_obj) $(nek_blas_obj) $(nek_cmt_obj) \
-                 $(nek_lapack_obj) $(nek_mpi_obj) $(nek_mxm_obj) $(nek_neknek_obj)
+nek_drive_obj  := $(addprefix $(objdir)/, drive.o)
+
+nek_core_f_obj := $(addprefix $(objdir)/, \
+                  drive1.o drive2.o plan4.o bdry.o coef.o conduct.o connect1.o connect2.o \
+                  dssum.o edgec.o eigsolv.o gauss.o genxyz.o navier1.o makeq.o navier0.o \
+                  navier2.o navier3.o navier4.o prepost.o speclib.o map2.o turb.o mvmesh.o ic.o \
+                  ssolv.o planx.o mxm_wrapper.o hmholtz.o gfdm_par.o  gfdm_op.o gfdm_solve.o \
+                  subs1.o subs2.o genbox.o gmres.o hsmg.o convect.o induct.o perturb.o navier5.o \
+                  navier6.o navier7.o navier8.o fast3d.o fasts.o calcz.o byte_mpi.o postpro.o \
+                  cvode_driver.o vprops.o qthermal.o cvode_aux.o makeq_aux.o papi.o nek_in_situ.o \
+                  readat_new.o @CASENAME@.o)
+
+nek_math_obj   := $(addprefix $(objdir)/, math.o)
+nek_blas_obj   := $(addprefix $(objdir)/, @nek_blas_obj@)   # blas.o | null
+nek_cmt_obj    := $(addprefix $(objdir)/, @nek_cmt_obj@)    # drive1_cmt.o ... | cmt_dummy.o
+nek_lapack_obj := $(addprefix $(objdir)/, @nek_lapack_obj@) # dsygv.o ssygv.o | null
+nek_mpi_obj    := $(addprefix $(objdir)/, @nek_mpi_obj@)    # byte_mpi.o comm_mpi.o | byte_mpi.o comm_mpi.o mpi_dummy.o
+nek_mxm_obj    := $(addprefix $(objdir)/, @nek_mxm_obj@)    # mxm_std.o | mxm_std.o mxm_bgq.o
+nek_neknek_obj := $(addprefix $(objdir)/, @nek_neknek_obj@) # singlmesh.o | multimesh.o
+
+nek_flib_obj   := $(nek_core_f_obj) $(nek_math_obj) $(nek_blas_obj) $(nek_cmt_obj) \
+                  $(nek_lapack_obj) $(nek_mpi_obj) $(nek_mxm_obj) $(nek_neknek_obj)
 
 # == C objects =====================================================================================
-nek_core_c_obj = $(addprefix $(objdir)/, \
-                 byte.o chelpers.o nek_comm.o finiparser.o iniparser.o dictionary.o)
+nek_core_c_obj := $(addprefix $(objdir)/, \
+                  byte.o chelpers.o nek_comm.o finiparser.o iniparser.o dictionary.o)
 
-jl_core_obj    = $(addprefix $(objdir)/$(jl_prefix), \
-                 gs.o sort.o sarray_transfer.o sarray_sort.o gs_local.o crystal.o comm.o tensor.o \
-                 fail.o fcrystal.o)
-jl_interp_obj  = $(addprefix $(objdir)/$(jl_prefix), \
-                 findpts.o findpts_local.o obbox.o poly.o lob_bnd.o findpts_el_3.o findpts_el_2.o)
-jl_cgs_obj     = $(addprefix $(objdir)/$(jl_prefix), @jl_cgs_obj@)
+jl_core_obj    := $(addprefix $(objdir)/$(jl_prefix), \
+                  gs.o sort.o sarray_transfer.o sarray_sort.o gs_local.o crystal.o comm.o tensor.o \
+                  fail.o fcrystal.o)
+jl_interp_obj  := $(addprefix $(objdir)/$(jl_prefix), \
+                  findpts.o findpts_local.o obbox.o poly.o lob_bnd.o findpts_el_3.o findpts_el_2.o)
+jl_cgs_obj     := $(addprefix $(objdir)/$(jl_prefix), @jl_cgs_obj@)
 
-nek_clib_obj   = $(nek_core_c_obj) $(jl_core_obj) $(jl_interp_obj) $(jl_cgs_obj)
+nek_clib_obj   := $(nek_core_c_obj) $(jl_core_obj) $(jl_interp_obj) $(jl_cgs_obj)
 
 # == Rules =========================================================================================
 nek5000: $(nek_drive_obj) $(nek_flib_obj) $(nek_clib_obj)