added openacc_fortran_options only for the compilation of Fortran codes

fixed a cmake style

added to two other components

src/horizontal/CMakeLists.txt

@@ -39,7 +39,9 @@ if(IM_ENABLE_OPENACC)
   # If _OPENACC is defined, assume that the required compiler flags are already
   # provided, e.g. in CMAKE_Fortran_FLAGS:
   if(NOT HAS_OPENACC_MACRO)
-    target_compile_options(iconmath-horizontal PRIVATE ${OpenACC_Fortran_OPTIONS})
+    target_compile_options(iconmath-horizontal
+                           PRIVATE
+                           $<$<COMPILE_LANGUAGE:Fortran>:${OpenACC_Fortran_OPTIONS}>)
     # This make sures that unit tests (FortUTF) compiles without the need of
     # passing OpenACC compile option.
     target_link_libraries(iconmath-horizontal PRIVATE OpenACC::OpenACC_Fortran)

src/interpolation/CMakeLists.txt

@@ -41,7 +41,8 @@ if(IM_ENABLE_OPENACC)
   # provided, e.g. in CMAKE_Fortran_FLAGS:
   if(NOT HAS_OPENACC_MACRO)
     target_compile_options(iconmath-interpolation
-                           PRIVATE ${OpenACC_Fortran_OPTIONS})
+                           PRIVATE
+                           $<$<COMPILE_LANGUAGE:Fortran>:${OpenACC_Fortran_OPTIONS}>)
     # This make sures that unit tests (FortUTF) compiles without the need of
     # passing OpenACC compile option.
     target_link_libraries(iconmath-interpolation PRIVATE OpenACC::OpenACC_Fortran)

src/support/CMakeLists.txt

@@ -50,7 +50,9 @@ if(IM_ENABLE_OPENACC)
   # If _OPENACC is defined, assume that the required compiler flags are already
   # provided, e.g. in CMAKE_Fortran_FLAGS:
   if(NOT HAS_OPENACC_MACRO)
-    target_compile_options(iconmath-support PRIVATE ${OpenACC_Fortran_OPTIONS})
+    target_compile_options(iconmath-support
+                           PRIVATE
+                           $<$<COMPILE_LANGUAGE:Fortran>:${OpenACC_Fortran_OPTIONS}>)
     # This make sures that unit tests (FortUTF) compiles without the need of
     # passing OpenACC compile option.
     target_link_libraries(iconmath-support PRIVATE OpenACC::OpenACC_Fortran)