cmake: rework gurobi support

CMakeLists.txt

@@ -235,6 +235,10 @@ if(USE_GLPK)
   message(STATUS "Build GLPK: ${BUILD_GLPK}")
 endif()
 
+## GUROBI
+# Since it is dynamicaly loaded upon use, OFF is currently not supported.
+CMAKE_DEPENDENT_OPTION(USE_GUROBI "Use the Gurobi solver" ON "BUILD_CXX" OFF)
+
 ## HiGHS
 # see: https://github.com/ERGO-Code/HiGHS
 CMAKE_DEPENDENT_OPTION(USE_HIGHS "Use the HiGHS solver" OFF "BUILD_CXX" OFF)

cmake/cpp.cmake

@@ -52,6 +52,9 @@ if(USE_GLPK)
   list(APPEND OR_TOOLS_COMPILE_DEFINITIONS "USE_GLPK")
   set(GLPK_DIR glpk)
 endif()
+if(USE_GUROBI)
+  set(GUROBI_DIR gurobi)
+endif()
 if(USE_HIGHS)
   list(APPEND OR_TOOLS_COMPILE_DEFINITIONS "USE_HIGHS")
 endif()
@@ -283,7 +286,7 @@ foreach(SUBPROJECT IN ITEMS
  ${GSCIP_DIR}
  glop
  graph
- gurobi
+ ${GUROBI_DIR}
  init
  linear_solver
  lp_data