pythongh-89792: unhardcode freeze test build parallelism.

base it on the number of cpus, don't use more than max(2, 2/3).

Tools/freeze/test/freeze.py

@@ -163,16 +163,25 @@ def prepare(script=None, outdir=None):
     if not MAKE:
         raise UnsupportedError('make')
 
+    cores = os.cpu_count()
+    if cores and cores >= 3:
+        # this test is most often run as part of the whole suite with a lot
+        # of other tests running in parallel, from 1-2 vCPU systems up to
+        # people's NNN core beasts. Don't attempt to use it all.
+        parallel = f'-j{cores*2//3}'
+    else:
+        parallel = '-j2'
+
     # Build python.
-    print(f'building python in {builddir}...')
+    print(f'building python {parallel=} in {builddir}...')
     if os.path.exists(os.path.join(srcdir, 'Makefile')):
         # Out-of-tree builds require a clean srcdir.
         _run_quiet([MAKE, '-C', srcdir, 'clean'])
-    _run_quiet([MAKE, '-C', builddir, '-j8'])
+    _run_quiet([MAKE, '-C', builddir, parallel])
 
     # Install the build.
     print(f'installing python into {prefix}...')
-    _run_quiet([MAKE, '-C', builddir, '-j8', 'install'])
+    _run_quiet([MAKE, '-C', builddir, 'install'])
     python = os.path.join(prefix, 'bin', 'python3')
 
     return outdir, scriptfile, python