use variables CLANG, GCC, LINUX in CMake code

Base/CMakeLists.txt

@@ -35,15 +35,15 @@ target_include_directories(${lib}
 
 # g++ versions less than 9.1 need to link against libstdc++fs
 # if std::filesystem is used
-if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
+if(GCC
     AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.1)
     target_link_libraries(${lib} PRIVATE stdc++fs)
 endif()
 # the same applies to clang versions less than 9.0: they need to link
 # against libstdc++fs or libc++fs if std::filesystem is used
-if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang"
+if(CLANG
     AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0)
-  if(CMAKE_HOST_SYSTEM_NAME STREQUAL "Linux")
+  if(LINUX)
     target_link_libraries(${lib} PRIVATE stdc++fs)
   else()
     target_link_libraries(${lib} PRIVATE c++fs)

Tests/Unit/Numeric/CMakeLists.txt

@@ -13,7 +13,7 @@ target_include_directories(${test} PUBLIC
     ${CMAKE_SOURCE_DIR}/3rdparty/common/gtest/gtest-1.8.0/include
     ${CMAKE_SOURCE_DIR}/Tests/Unit/utilities)
 target_link_libraries(${test} ${BornAgainCore_LIBRARY} gtest)
-if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+if(GCC)
     target_compile_options(${test} PUBLIC "-Wno-deprecated-copy")
 endif()
 

cmake/BornAgain/MakeLib.cmake

@@ -3,7 +3,7 @@
 function(MakeLib name lib tmpdir withPython)
 
     if(withPython)
-        if((CMAKE_CXX_COMPILER_ID STREQUAL "Clang") OR (CMAKE_CXX_COMPILER_ID STREQUAL "GNU"))
+        if((CLANG) OR (GCC))
             # suppress warnings from auto-generated code (last updated for Swig 4.0.1)
             set_source_files_properties(${AUTO_DIR}/lib${lib}_wrap.cpp
                 PROPERTIES COMPILE_OPTIONS

cmake/commons/CoverageFunction.cmake

@@ -43,7 +43,7 @@ else()
     message(FATAL_ERROR "C compiler is not GNU; don't know how to set code coverage flags!")
 endif()
 
-if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+if(GCC)
     string(APPEND CMAKE_CXX_FLAGS " -coverage")
 else()
     message(FATAL_ERROR "CXX compiler is not GNU; don't know how to set code coverage flags!")

cmake/commons/DebugOptimization.cmake

@@ -22,7 +22,7 @@ else()
   message(WARNING "C compiler is not GNU; debug optimization has no effect")
 endif()
 
-if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+if(GCC)
   string(APPEND CMAKE_CXX_FLAGS " -Og")
 else()
   message(WARNING "C compiler is not GNU; debug optimization has no effect")