In much of the F95 binding (and probably the F77 as well), integers are declared without a kind parameter. This will result in incorrect results for compilers where the C int type and the Fortran default integer are not of the same length (e.g. the 64-bit version of g95).
strutil.f90 will not compile on such a system as the islen function is declared as integer*4 in one place and default integer in another.
I would suggest, defining a plint kind that is set to be equal to c_int from iso_c_binding for f95+. For f77 probably the only viable fix is to declare all integers to be integer*4.