gperftools: add a test for plain malloc() support

[valgur]

Adds MALLOCSTATS=1 env var, which enable malloc statistics on program termination:

gperftools/2.15 (test package): RUN: ./test_package_indirect
------------------------------------------------
MALLOC:          90112 (    0.1 MiB) Bytes in use by application
MALLOC: +       942080 (    0.9 MiB) Bytes in page heap freelist
MALLOC: +        16264 (    0.0 MiB) Bytes in central cache freelist
MALLOC: +            0 (    0.0 MiB) Bytes in transfer cache freelist
MALLOC: +          120 (    0.0 MiB) Bytes in thread cache freelists
MALLOC: +      2490368 (    2.4 MiB) Bytes in malloc metadata
MALLOC:   ------------
MALLOC: =      3538944 (    3.4 MiB) Actual memory used (physical + swap)
MALLOC: +            0 (    0.0 MiB) Bytes released to OS (aka unmapped)
MALLOC:   ------------
MALLOC: =      3538944 (    3.4 MiB) Virtual address space used
MALLOC:
MALLOC:              7              Spans in use
MALLOC:              2              Thread heaps in use
MALLOC:           8192              Tcmalloc page size
------------------------------------------------
Call ReleaseFreeMemory() to release freelist memory to the OS (via madvise()).
Bytes released to the OS take up virtual address space but no physical memory.

This allows the use of plain malloc() to be tested in a verifiable manner in addition to the existing direct tc_malloc() functions from an included header.

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 3 (8a4acc46d1d2039397246bbc964e243c66a6a90b):

• gperftools/2.14.0:
  All packages built successfully! (All logs)

• gperftools/2.15:
  All packages built successfully! (All logs)

• gperftools/2.13.0:
  All packages built successfully! (All logs)

• gperftools/2.11.0:
  All packages built successfully! (All logs)

• gperftools/2.12.0:
  All packages built successfully! (All logs)

• gperftools/2.10.0:
  All packages built successfully! (All logs)

---

Conan v2 pipeline ✔️

Note: Conan v2 builds are now mandatory. Please read our discussion about it.

All green in build 3 (8a4acc46d1d2039397246bbc964e243c66a6a90b):

• gperftools/2.15:
  All packages built successfully! (All logs)

• gperftools/2.13.0:
  All packages built successfully! (All logs)

• gperftools/2.14.0:
  All packages built successfully! (All logs)

• gperftools/2.11.0:
  All packages built successfully! (All logs)

• gperftools/2.12.0:
  All packages built successfully! (All logs)

• gperftools/2.10.0:
  All packages built successfully! (All logs)