gprofng: fix infinite recursion on calloc with multi-threaded applications

libcollector uses pthread_getspecific() and pthread_setspecific() to access
thread local memory. libcollector uses this memory to check that
interposed functions (like malloc, calloc or free) don't have recursion.
The first time we call calloc(), we call pthread_setspecific() to create
a thread-specific value.
On Ubuntu machine, pthread_setspecific() calls calloc(), and we cannot intercept
such recursion.
gcc supports thread-local storage. For example,
  static __thread int reentrance = 0;
I rewrote code using this instead of pthread_setspecific().

gprofng/ChangeLog
2024-03-23  Vladimir Mezentsev  <vladimir.mezentsev@oracle.com>

	PR gprofng/31460
	* libcollector/heaptrace.c: Use the __thread variable to check for
	* reentry. Clean up code.