[7ca0fdf] Disable munmap() if it causes VM map holes

[Mike Hommey]

Hi,

I noticed something "interesting" with the test for VM map holes:
If I compile it manually, it fails:

  Hoped for 0x7f835133d000, got 0x7f8350b3d000
  0x7f835173d000..0x7f835133d000..0x7f8350f3d000..0x7f835073d000..0x7f8350b3d000

Apparently, this happens when *not* linking libm to the testcase. It
also does happen when linking libm and some other library (tried
pthread and stdc++).

Moreover, the test being run on the build machine, which can have a very
different setup from the machine the binary runs on, it is most probably
not reliable to decide whether to disable munmap or not.

Mike