x64: Fix stack alignment in fault handlers

Make sure stack pointer is 16-byte aligned. Spotted by Nadav.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
mmu: Anonymous memory demand paging

Switch to demand paging for anonymous virtual memory.

  SPECjvm 2008 (higher is better):

                          ops/m
  benchmark               master  paging  +/- %

  compiler.compiler       347.06  356.94   +2.8
  compiler.sunflow        132.17  134.12   +1.5
  compress                107.59  123.26  +14.6
  crypto.aes               41.92   42.14   +0.5
  crypto.rsa              217.27  218.34   +0.5
  crypto.signverify       201.62  184.31   -8.6
  derby                   184.81  185.52   +0.4
  mpegaudio                78.86   80.40   +2.0
  scimark.fft.large        35.91   35.78   -0.4
  scimark.lu.large         14.36   16.74  +16.6
  scimark.sor.large        26.16   25.98   -0.7
  scimark.sparse.large     37.64   38.61   +2.6
  scimark.fft.small       176.99  207.07  +17.0
  scimark.lu.small        222.76  244.56   +9.8
  scimark.sor.small       115.81  116.77   +0.8
  scimark.sparse.small    119.97  125.31   +4.5
  scimark.monte_carlo     141.17  139.64   -1.1
  serial                  100.48   97.20   -3.3
  sunflow                  79.54   84.55   +6.3
  xml.transform           217.30  217.59   +0.1
  xml.validation          349.88  348.65   -0.4

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
tst-mmap.so: mincore() tests for demand paging

As suggested by Nadav, add tests for mincore() interraction with demand
paging.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>