Avoid memory exhaustion during the execution of unit tests.
The limited number of iterations reduced the memory consumption
of GNU debugger from hundreds of GBs to hundreds of MBs.
The test case try to load a core file with many program headers
(mmap allocations). The hypothesis is that loading this core
file either hits an edge case of libc allocator, or it exhausts
the virtual address space as the memory overcommitment is not
allowed on Solaris; there is a physical storage for each byte
of allocated memory...

Not suitable for upstream.

--- gdb-13.1/gdb/testsuite/gdb.base/many-headers.c
+++ gdb-13.1/gdb/testsuite/gdb.base/many-headers.c
@@ -25,7 +25,7 @@ {
   char *ptr;
   int ind, cnt;
 
-  cnt = 100000;
+  cnt = 1000;
   for (ind = 0; ind < cnt; ind++)
     {
       ptr = mmap (NULL, 100, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);