[CMakeLists.txt] remove references to C since CXX is the only way to build the project

CMakeLists.txt

@@ -76,9 +76,7 @@ set(CMAKE_INSTALL_RPATH "${CMAKE_SOURCE_DIR}")
 add_definitions(-DUSE_CMAKE_LIBS)
 
 if(MSVC)
-  set(CMAKE_C_FLAGS "/wd4013 /wd4018 /wd4028 /wd4047 /wd4068 /wd4090 /wd4101 /wd4113 /wd4133 /wd4190 /wd4244 /wd4267 /wd4305 /wd4477 /wd4996 /fp:fast ${CMAKE_C_FLAGS}")
   set(CMAKE_CXX_FLAGS "/wd4013 /wd4018 /wd4028 /wd4047 /wd4068 /wd4090 /wd4101 /wd4113 /wd4133 /wd4190 /wd4244 /wd4267 /wd4305 /wd4477 /wd4996 /fp:fast ${CMAKE_CXX_FLAGS}")
-  string(REGEX REPLACE "/O2" "/Ox" CMAKE_C_FLAGS_RELEASE ${CMAKE_C_FLAGS_RELEASE})
   string(REGEX REPLACE "/O2" "/Ox" CMAKE_CXX_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
   add_definitions(-D_CRT_RAND_S)
   add_definitions(-DNOMINMAX)
@@ -86,21 +84,15 @@ if(MSVC)
 endif()
 
 if(CMAKE_COMPILER_IS_GNUCC)
-  set(CMAKE_C_FLAGS "-Wno-unused-result -Wno-discarded-qualifiers -Wno-incompatible-pointer-types ${CMAKE_C_FLAGS}")
   set(CMAKE_CXX_FLAGS "-Wno-unused-result -Wno-write-strings ${CMAKE_CXX_FLAGS}")
-  string(REGEX REPLACE "-O0" "-Og" CMAKE_C_FLAGS_DEBUG ${CMAKE_C_FLAGS_DEBUG})
   string(REGEX REPLACE "-O0" "-Og" CMAKE_CXX_FLAGS_DEBUG ${CMAKE_CXX_FLAGS_DEBUG})
-  string(REGEX REPLACE "-O3" "-Ofast" CMAKE_C_FLAGS_RELEASE ${CMAKE_C_FLAGS_RELEASE})
   string(REGEX REPLACE "-O3" "-Ofast" CMAKE_CXX_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
-  set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -ffp-contract=fast -mavx -mavx2 -msse3 -msse4.1 -msse4.2 -msse4a")
   set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -ffp-contract=fast -mavx -mavx2 -msse3 -msse4.1 -msse4.2 -msse4a")
 endif()
 
 if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
   set(CMAKE_CXX_FLAGS "-Wno-deprecated -Wno-writable-strings ${CMAKE_CXX_FLAGS}")
-  string(REGEX REPLACE "-O0" "-Og" CMAKE_C_FLAGS_DEBUG ${CMAKE_C_FLAGS_DEBUG})
   string(REGEX REPLACE "-O0" "-Og" CMAKE_CXX_FLAGS_DEBUG ${CMAKE_CXX_FLAGS_DEBUG})
-  string(REGEX REPLACE "-O3" "-Ofast" CMAKE_C_FLAGS_RELEASE ${CMAKE_C_FLAGS_RELEASE})
   string(REGEX REPLACE "-O3" "-Ofast" CMAKE_CXX_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE})
 endif()
 
@@ -168,10 +160,13 @@ if(MSVC)
   include_directories(${PTHREADS_INCLUDE_DIR})
 endif()
 
-find_package(OpenMP)
-if(OPENMP_FOUND)
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
+if(${CMAKE_VERSION} VERSION_LESS "3.9.0")
+  message(WARNING "To build with OpenMP support you need CMake 3.9.0+")
+else()
+  find_package(OpenMP)
+  if(OPENMP_FOUND)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
+  endif()
 endif()
 
 #look for all *.h files in src folder
@@ -252,8 +247,8 @@ if(OpenCV_FOUND)
 endif()
 
 if(OPENMP_FOUND)
-  target_link_libraries(darknet OpenMP::OpenMP_C)
-  target_link_libraries(darklib OpenMP::OpenMP_C)
+  target_link_libraries(darknet OpenMP::OpenMP_CXX)
+  target_link_libraries(darklib OpenMP::OpenMP_CXX)
 endif()
 
 if(CMAKE_COMPILER_IS_GNUCC)