fix(fpm_compiler_arguments): add IBM XL Fortran compile command

Author: rouson

test/compiler_test_m.f90

@@ -237,6 +237,8 @@ function fpm_compiler_arguments() result(args)
           args = "--archiver ar --compiler xlf2008_r --flag -DXLF"
         else if (index(compiler_identity, "Cray")==1) then
           args = "--compiler ftn"
+        else if (index(compiler_identity, "XLF")==1) then
+          args = "--compiler xlf2008_r"
         else
           error stop "----> Unrecognized compiler_version() in function fpm_compiler_arguments. <----"
         end if