Windows: Replace system calls with equivalent Fortran/C calls

Fix intermittent failure of `system` commands on Windows: occasionally the system calls would fail to finish and make the program hang or end prematurely without any error message.

modules/nwtc-library/src/SysIVF.f90

@@ -193,18 +193,18 @@ END SUBROUTINE Get_CWD
 !> This routine creates a given directory if it does not already exist.
 SUBROUTINE MKDIR ( new_directory_path )
 
+   USE IFPORT, ONLY: MAKEDIRQQ
    implicit none
 
    character(*), intent(in) :: new_directory_path
-   character(1024)          :: make_command
    logical                  :: directory_exists
+   logical                  :: success
 
    ! Check if the directory exists first
    inquire( directory=trim(new_directory_path), exist=directory_exists )
 
    if ( .NOT. directory_exists ) then
-      make_command = 'mkdir "'//trim(new_directory_path)//'"'
-      call system( make_command )
+      success = MAKEDIRQQ( trim(new_directory_path) )
    endif
 
 END SUBROUTINE MKDIR