*: adjust build system to fix std::filesystem compiler errors

This commit updates the build system to link libstdc++fs if building
on Lanka. This might not be needed for local development on Mac's, so
it is hidden behind a flag. Set LANKA=ON before `make` to link it.

Author: Rohan Yadav

Makefile

@@ -17,6 +17,10 @@ TACO_OUT = results/taco/$(benches_name)benches_$(shell date +%Y_%m_%d_%H%M%S).cs
 
 GRAPHBLAS := "OFF"
 OPENMP := "OFF"
+# Set LANKA=ON if compiling on the MIT Lanka cluster.
+ifeq ($(LANKA),)
+LANKA := "OFF"
+endif
 
 export TACO_TENSOR_PATH = data/
 
@@ -59,7 +63,7 @@ ifeq ($(VALIDATION_OUTPUT_PATH),)
 endif
 
 taco/build/taco-bench: results check-and-reinit-submodules taco/benchmark/googletest
-	mkdir -p taco/build/ && cd taco/build/ && cmake -DOPENMP=$(OPENMP) -DGRAPHBLAS=$(GRAPHBLAS) ../ && $(MAKE) taco-bench 
+	mkdir -p taco/build/ && cd taco/build/ && cmake -DOPENMP=$(OPENMP) -DGRAPHBLAS=$(GRAPHBLAS) -DLANKA=$(LANKA) ../ && $(MAKE) taco-bench 
 
 taco/benchmark/googletest: check-and-reinit-submodules
 	if [ ! -d "taco/benchmark/googletest" ] ; then git clone https://github.com/google/googletest taco/benchmark/googletest; fi

taco/CMakeLists.txt

@@ -2,6 +2,7 @@ cmake_minimum_required(VERSION 2.8.12 FATAL_ERROR)
 project(taco-bench)
 set(CMAKE_BUILD_TYPE "release")
 option(GRAPHBLAS "Build GraphBLAS benchmarks" OFF)
+option(LANKA "Build benchmarks for the Lanka cluster." OFF)
 
 if(GRAPHBLAS)
   message("-- Will build GraphBLAS benchmarks")
@@ -22,7 +23,11 @@ set(CMAKE_CXX_FLAGS "${C_CXX_FLAGS} -std=c++14")
 
 add_executable(taco-bench ${TEST_SOURCES} bench.h)
 target_link_libraries(taco-bench benchmark::benchmark)
-target_link_libraries(taco-bench taco)
+target_link_libraries(taco-bench taco)4
+# Only link stdc++fs on lanka. Mac's don't need this set.
+if (LANKA)
+  target_link_libraries(taco-bench stdc++fs)
+endif(LANKA)
 if(GRAPHBLAS)
   target_link_libraries(taco-bench graphblas)
 endif(GRAPHBLAS)