v1: Initial version
v2: implement review comments
v3: adapt to new API

The current sleep timer implementation basically offers two variants. Either
wait the specified time exactly with a condition variable (as host) or use a
combination of it with a thread yielding busy loop afterwards (usleep timer).

While the second one is very precise it consumes CPU loops for each wait call
below 50us. Games like Bomberman Ultra spam 30us waits and the emulator hogs
low power CPUs. Switching to host mode reduces CPU consumption but gives a
~50us penalty for each wait call. Thus extending all sleeps by a factor of
more than two.

The following bugfix tries to improve the system timer for Linux by using
Linux native timers for small wait calls below 1ms. This has two effects.

- Host wait setting has much less wait overhead
- usleep wait setting produces lower CPU overhead

Some numbers for host timer setting from my tests on a Pentium G5600, UHD
630 waiting in the Bomberman welcome screen. I shortened/lengthened the
game timer inside the emulator to get a better picture for different wait
lenghts. As you can see current implementation always produces a 50us
overhead while the new implementation mostly stays below 10us. us(er),
sy(stem), id(le) have been taken from vmstat during the tests.

sleeps of 70usec
              Calls   >=120us  <120us   <95us   <80us   <73us  us  sy  id
Master run 1: 1000000  708599  144933  114607   27954    3906  44  12  15
Master run 2: 1000000  707853  145802  114613   27757    3975  45  12  43
Patch  run 1: 1000000   24478   37779  122771  679292  135679  46  13  41
Patch  run 2: 1000000   27544   38647  120150  676306  137353  45  13  42

sleeps of 60usec
              Calls   >=110us  <110us   <85us   <70us   <63us  us  sy  id
Master run 1: 1000000  695187  167665  107111   26767    3269  42  11  47
Master run 2: 1000000  698397  166151  106322   25889    3241  42  11  46
Patch  run 1: 1000000   23266   36454  131397  651232  157650  44  12  44
Patch  run 2: 1000000   27780   41361  141313  636585  152961  45  12  42

sleeps of 50usec
              Calls   >=100us  <100us   <75us   <60us   <53us  us  sy  id
Master run 1: 1000000  690729  183766   97207   25160    3137  43  12  46
Master run 2: 1000000  689518  184570   97716   25131    3065  42  11  47
Patch  run 1: 1000000   21068   34504  124814  646399  173214  45  13  42
Patch  run 2: 1000000   22531   36852  130585  638397  171635  44  12  44

sleeps of 40usec
              Calls    >=90us   <90us   <65us   <50us   <43us  us  sy  id
Master run 1: 1000000  688084  176572  111680   20357    3306  45  12  44
Master run 2: 1000000  687553  177216  111599   20409    3223  46  12  42
Patch  run 1: 1000000   18164   31248  113778  643851  192958  44  12  44
Patch  run 2: 1000000   20985   34841  120508  633031  190635  45  12  43

sleeps of 30usec
              Calls    >=80us   <80us   <55us   <40us   <33us  us  sy  id
Master run 1: 1000000  721705  205084   60793   12060     357  44  12  45
Master run 2: 1000000  720323  205960   61524   11884     309  43  11  46
Patch  run 1: 1000000   15139  16863   101604  629094  227299  44  12  44
Patch  run 2: 1000000   18560  30207   110159  617093  223981  45  12  43

sleeps of 20usec
              Calls    >=70us   <70us   <45us   <30us   <23us  us  sy  id
Master run 1: 1000000  813648  144746   36458    5111      36  43  12  45
Master run 2: 1000000  813322  144917   36618    5097      46  45  12  43
Patch  run 1: 1000000   14073   23076   83921  635412  243517  45  13  42
Patch  run 2: 1000000   13769   23460   86245  632826  243700  44  13  43

sleeps of 10usec
              Calls    >=60us   <60us   <35us   <20us   <13us  us  sy  id
Master run 1: 1000000  864216  101101   29002    5651      29  43  12  45
Master run 2: 1000000  864896  100595   28941    5550      18  42  11  47
Patch  run 1: 1000000    7613   13301   52335  640861  285889  46  13  41
Patch  run 2: 1000000    7223   13280   52123  644643  282731  47  13  40

Comparison between host and usleep setting for game defaults of 30us waits
                   fps  us  sy  id
Mater run host  :   53  43  11  46
Patch run host  :   52  44  12  44
Mater run usleep:   49  51  18  31
Patch run usleep:   51  48  15  37

Implement Nekotekinas requests.