DEBUG: tools: add vma_set_name() helper

DEBUG: tools: add vma_set_name() helper

Following David Carlier's work in 98d22f21 ("MEDIUM: shctx: Naming shared
memory context"), let's provide an helper function to set a name hint on
a virtual memory area (ie: anonymous map created using mmap(), or memory
area returned by malloc()).

Naming will only occur if available, and naming errors will be ignored.
The function takes mandatory <type> and <name> parameterss to build the
map name as follow: "type:name". When looking at /proc/<pid>/maps, vma
named using this helper function will show up this way (provided that
the kernel has prtcl support for PR_SET_VMA_ANON_NAME):

example, using mmap + MAP_SHARED|MAP_ANONYMOUS:
  7364c4fff000-736508000000 rw-s 00000000 00:01 3540  [anon_shmem:type:name]
Another example, using mmap + MAP_PRIVATE|MAP_ANONYMOUS or using
glibc/malloc() above MMAP_THRESHOLD:
  7364c4fff000-736508000000 rw-s 00000000 00:01 3540  [anon:type:name]