[v0.30] Build pciutils only if neccesary

If only HSA is enabled we dont need pciutils since AMD detection does
not rely on it. Therefore we change CMakeLists.txt to build pciutils
only if required.

This commit has some side-effects:
1. We now don't build Intel backend by default. In other words, no
   backend is built by default, the user must specify which backend
   to use.
2. There were some issues with includes and wrongly used defines and
   variables. This commit fixes all that.

CMakeLists.txt

@@ -10,9 +10,10 @@ set(CUDA_DIR "${SRC_DIR}/cuda")
 set(HSA_DIR "${SRC_DIR}/hsa")
 set(INTEL_DIR "${SRC_DIR}/intel")
 
-# Enable Intel backend by default
-if(NOT DEFINED ENABLE_INTEL_BACKEND)
-    set(ENABLE_INTEL_BACKEND true)
+# Make sure that at least one backend is enabled.
+# It does not make sense that the user has not specified any backend.
+if(NOT ENABLE_INTEL_BACKEND AND NOT ENABLE_CUDA_BACKEND AND NOT ENABLE_HSA_BACKEND)
+  message(FATAL_ERROR "No backend was enabled! Please enable at least one backend with -DENABLE_XXX_BACKEND")
 endif()
 
 if(ENABLE_CUDA_BACKEND)
@@ -66,35 +67,63 @@ if(ENABLE_HSA_BACKEND)
   endif()
 endif()
 
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake")
-find_package(PCIUTILS)
-if(NOT ${PCIUTILS_FOUND})
-  message(STATUS "${BoldYellow}pciutils not found, downloading and building a local copy...${ColorReset}")
+set(GPUFECH_COMMON
+    ${COMMON_DIR}/main.cpp
+    ${COMMON_DIR}/args.cpp
+    ${COMMON_DIR}/gpu.cpp
+    ${COMMON_DIR}/global.cpp
+    ${COMMON_DIR}/printer.cpp
+    ${COMMON_DIR}/master.cpp
+    ${COMMON_DIR}/uarch.cpp
+)
 
-  # Download and build pciutils
-  set(PCIUTILS_INSTALL_LOCATION ${CMAKE_BINARY_DIR}/pciutils-install)
-  ExternalProject_Add(pciutils
-    GIT_REPOSITORY https://github.com/pciutils/pciutils
-    CONFIGURE_COMMAND ""
-    BUILD_COMMAND make SHARED=no HWDB=no
-    BUILD_IN_SOURCE true
-    INSTALL_COMMAND make PREFIX=${PCIUTILS_INSTALL_LOCATION} install-lib
-  )
+set(GPUFETCH_LINK_TARGETS z)
 
-  include_directories(${PCIUTILS_INSTALL_LOCATION}/include)
-  link_directories(${PCIUTILS_INSTALL_LOCATION}/lib)
-else()
-  include_directories(${PCIUTILS_INCLUDE_DIR})
-  link_libraries(${PCIUTILS_LIBRARIES})
-  # Needed for linking libpci in FreeBSD
-  link_directories(/usr/local/lib/)
+if(NOT(ENABLE_HSA_BACKEND AND NOT ENABLE_CUDA_BACKEND AND NOT ENABLE_INTEL_BACKEND))
+  # Look for pciutils only if not building HSA only.
+  #
+  # This has the (intented) secondary effect that if only HSA backend is enabled
+  # by the user, but ROCm cannot be found, pciutils will still be compiled in
+  # order to show the list of GPUs available on the system, so that the user will
+  # get at least some feedback even if HSA is not found.
+  list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake")
+  list(APPEND GPUFECH_COMMON ${COMMON_DIR}/pci.cpp ${COMMON_DIR}/sort.cpp)
+  list(APPEND GPUFETCH_LINK_TARGETS pci)
+  set(CMAKE_ENABLE_PCIUTILS ON)
+
+  find_package(PCIUTILS)
+  if(NOT ${PCIUTILS_FOUND})
+    message(STATUS "${BoldYellow}pciutils not found, downloading and building a local copy...${ColorReset}")
+
+    # Download and build pciutils
+    set(PCIUTILS_INSTALL_LOCATION ${CMAKE_BINARY_DIR}/pciutils-install)
+    ExternalProject_Add(pciutils
+      GIT_REPOSITORY https://github.com/pciutils/pciutils
+      CONFIGURE_COMMAND ""
+      BUILD_COMMAND make SHARED=no HWDB=no
+      BUILD_IN_SOURCE true
+      INSTALL_COMMAND make PREFIX=${PCIUTILS_INSTALL_LOCATION} install-lib
+    )
+
+    include_directories(${PCIUTILS_INSTALL_LOCATION}/include)
+    link_directories(${PCIUTILS_INSTALL_LOCATION}/lib)
+  else()
+    include_directories(${PCIUTILS_INCLUDE_DIR})
+    link_libraries(${PCIUTILS_LIBRARIES})
+    # Needed for linking libpci in FreeBSD
+    link_directories(/usr/local/lib/)
+  endif()
 endif()
 
-add_executable(gpufetch ${COMMON_DIR}/main.cpp ${COMMON_DIR}/args.cpp ${COMMON_DIR}/gpu.cpp ${COMMON_DIR}/pci.cpp ${COMMON_DIR}/sort.cpp ${COMMON_DIR}/global.cpp ${COMMON_DIR}/printer.cpp ${COMMON_DIR}/master.cpp ${COMMON_DIR}/uarch.cpp)
+add_executable(gpufetch ${GPUFECH_COMMON})
 set(SANITY_FLAGS -Wfloat-equal -Wshadow -Wpointer-arith -Wall -Wextra -pedantic -fstack-protector-all -pedantic)
 target_compile_features(gpufetch PRIVATE cxx_std_11)
 target_compile_options(gpufetch PRIVATE ${SANITY_FLAGS})
 
+if (CMAKE_ENABLE_PCIUTILS)
+  target_compile_definitions(gpufetch PUBLIC BACKEND_USE_PCI)
+endif()
+
 if(ENABLE_INTEL_BACKEND)
   target_compile_definitions(gpufetch PUBLIC BACKEND_INTEL)
 
@@ -156,7 +185,7 @@ if(ENABLE_HSA_BACKEND)
   target_link_libraries(gpufetch hsa_backend)
 endif()
 
-target_link_libraries(gpufetch pci z)
+target_link_libraries(gpufetch ${GPUFETCH_LINK_TARGETS})
 install(TARGETS gpufetch DESTINATION bin)
 
 if(NOT WIN32)