mount: optional support for -vv verbosity

mount: optional support for -vv verbosity
mount: do "struct globals" trick

With -vv on:

function                                             old     new   delta
verbose_mount                                          -      83     +83
mount_main                                           970     988     +18
mount_it_now                                         219     229     +10
singlemount                                         4564    4570      +6
mount_option_str                                     227     233      +6
nfs_mount_version                                      1       -      -1
fslist                                                 4       -      -4
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(add/remove: 1/2 grow/shrink: 4/0 up/down: 123/-5)            Total: 118 bytes