fix: Add -cpp flag support for flang-new compiler (#1169)

Author: perazz

src/fpm_compiler.F90

@@ -519,7 +519,7 @@ pure subroutine set_cpp_preprocessor_flags(id, flags)
     select case(id)
     case default
         flag_cpp_preprocessor = ""
-    case(id_caf, id_gcc, id_f95, id_nvhpc)
+    case(id_caf, id_gcc, id_f95, id_nvhpc, id_flang_new)
         flag_cpp_preprocessor = "-cpp"
     case(id_intel_classic_windows, id_intel_llvm_windows)
         flag_cpp_preprocessor = "/fpp"