reverse the pre-processor logic of the LRT mode define

with this change, the USER-INTEL package can be installed and
compiled without having to alter makefiles for adding -lpthread.
All "intel optimized" makefiles have been updated to have the
LRT feature enabled. This change will allow us to include the
USER-INTEL package in several automated testing configurations
and thus allows to detect incompatibilities and compilation issus faster.

doc/src/accelerate_intel.txt

@@ -361,10 +361,14 @@ intel"_package.html command that can improve performance when using
 "PPPM"_kspace_style.html for long-range electrostatics on processors
 with SMT. It generates an extra pthread for each MPI task. The thread
 is dedicated to performing some of the PPPM calculations and MPI
-communications. On Intel Xeon Phi x200 series CPUs, this will likely
+communications. This feature requires setting the preprocessor flag
-always improve performance, even on a single node. On Intel Xeon
+-DLMP_INTEL_USELRT in the makefile when compiling LAMMPS. It is unset
-processors, using this mode might result in better performance when
+in the default makefiles ({Makefile.mpi} and {Makefile.serial}) but
-using multiple nodes, depending on the machine. To use this mode,
+it is set in all makefiles tuned for the USER-INTEL package.  On Intel
+Xeon Phi x200 series CPUs, the LRT feature will likely improve
+performance, even on a single node. On Intel Xeon processors, using
+this mode might result in better performance when using multiple nodes,
+depending on the specific machine configuration. To enable LRT mode,
 specify that the number of OpenMP threads is one less than would
 normally be used for the run and add the "lrt yes" option to the "-pk"
 command-line suffix or "package intel" command. For example, if a run

doc/src/package.txt

@@ -335,7 +335,8 @@ from the USER-INTEL package is not used, then the LRT setting is
 ignored and no extra threads are generated. Enabling LRT will replace
 the "run_style"_run_style.html with the {verlet/lrt/intel} style that
 is identical to the default {verlet} style aside from supporting the
-LRT feature.
+LRT feature. This feature requires setting the preprocessor flag
+-DLMP_INTEL_USELRT in the makefile when compiling LAMMPS.
 
 The {balance} keyword sets the fraction of "pair
 style"_pair_style.html work offloaded to the coprocessor for split

src/MAKE/OPTIONS/Makefile.intel_coprocessor

@@ -9,7 +9,7 @@ SHELL = /bin/sh
 CC =		mpiicpc 
 MIC_OPT =       -qoffload-option,mic,compiler,"-fp-model fast=2 -mGLOB_default_function_attrs=\"gather_scatter_loop_unroll=4\""
 CCFLAGS =	-g -O3 -qopenmp -DLMP_INTEL_OFFLOAD -DLAMMPS_MEMALIGN=64 \
-                -xHost -fno-alias -ansi-alias -restrict \
+                -xHost -fno-alias -ansi-alias -restrict -DLMP_INTEL_USELRT \
                 -qoverride-limits $(MIC_OPT)
 SHFLAGS =	-fPIC
 DEPFLAGS =	-M

src/MAKE/OPTIONS/Makefile.intel_cpu_intelmpi

@@ -9,7 +9,7 @@ SHELL = /bin/sh
 CC =		mpiicpc 
 OPTFLAGS =      -xHost -O2 -fp-model fast=2 -no-prec-div -qoverride-limits
 CCFLAGS =	-qopenmp -DLAMMPS_MEMALIGN=64 -qno-offload \
-                -fno-alias -ansi-alias -restrict $(OPTFLAGS)
+                -fno-alias -ansi-alias -restrict $(OPTFLAGS) -DLMP_INTEL_USELRT
 SHFLAGS =	-fPIC
 DEPFLAGS =	-M
 

src/MAKE/OPTIONS/Makefile.intel_cpu_mpich

@@ -9,7 +9,7 @@ SHELL = /bin/sh
 CC =		mpicxx -cxx=icc
 OPTFLAGS =      -xHost -O2 -fp-model fast=2 -no-prec-div -qoverride-limits
 CCFLAGS =	-g -qopenmp -DLAMMPS_MEMALIGN=64 -no-offload \
-                -fno-alias -ansi-alias -restrict $(OPTFLAGS)
+                -fno-alias -ansi-alias -restrict $(OPTFLAGS) -DLMP_INTEL_USELRT
 SHFLAGS =	-fPIC
 DEPFLAGS =	-M
 

src/MAKE/OPTIONS/Makefile.intel_cpu_openmpi

@@ -10,7 +10,7 @@ export OMPI_CXX = icc
 CC =		mpicxx
 OPTFLAGS =      -xHost -O2 -fp-model fast=2 -no-prec-div -qoverride-limits
 CCFLAGS =	-g -qopenmp -DLAMMPS_MEMALIGN=64 -no-offload \
-                -fno-alias -ansi-alias -restrict $(OPTFLAGS)
+                -fno-alias -ansi-alias -restrict $(OPTFLAGS) -DLMP_INTEL_USELRT
 SHFLAGS =	-fPIC
 DEPFLAGS =	-M
 

src/MAKE/OPTIONS/Makefile.intel_knl_coprocessor

@@ -10,7 +10,7 @@ CC =		mpiicpc
 MIC_OPT =       -qoffload-arch=mic-avx512 -fp-model fast=2
 CCFLAGS =	-O3 -qopenmp -DLMP_INTEL_OFFLOAD -DLAMMPS_MEMALIGN=64 \
                 -xHost -fno-alias -ansi-alias -restrict \
-                -qoverride-limits $(MIC_OPT)
+                -qoverride-limits $(MIC_OPT) -DLMP_INTEL_USELRT
 SHFLAGS =	-fPIC
 DEPFLAGS =	-M
 

src/USER-INTEL/verlet_lrt_intel.h

@@ -23,7 +23,9 @@ IntegrateStyle(verlet/lrt/intel,VerletLRTIntel)
 #include "verlet.h"
 #include "pppm_intel.h"
 
-#ifndef LMP_INTEL_NOLRT
+#ifndef LMP_INTEL_USELRT
+#define LMP_INTEL_NOLRT
+#else
 
 #ifdef LMP_INTEL_LRT11
 #define _LMP_INTEL_LRT_11