Hard code the platform.py libc_ver() libc version for the pyston executable

this speeds up pip by several seconds because the pyston executable is very large.
CPython does not run into the problem because of the much smaller executable but has the same problem
when it has to retrieve the libc version of the pyston executable

from_cpython/Lib/platform.py

@@ -155,6 +155,10 @@ def libc_ver(executable=sys.executable,lib='',version='',
         The file is read and scanned in chunks of chunksize bytes.
 
     """
+    # Pyston change: hard code pyston executable libc version
+    if executable == sys.executable:
+        return ("glibc", "2.6")
+
     if hasattr(os.path, 'realpath'):
         # Python 2.2 introduced os.path.realpath(); it is used
         # here to work around problems with Cygwin not being