[4.8] OpenMP: Better CPU count detection for Linux

See b3cd55a4e23e443cc4561424e22c27fe7f05b5c1

Change-Id: Iafdee05e23c639fcd011550b38b2570670706c65

Author: Geunsik Lim <leemgs@gmail.com>
Date:   Tue Apr 2 19:56:53 2013 +0800
[4.8] Fix openmp support to use libgomp/config/linux

See a38e7b29885b25278b1d356b2efd21622376695d

Change-Id: I4e2671ea3aa8a67e9b5c6d5974b7486eb7ae54b7

Author: Andrew Hsieh <andrewhsieh@google.com>
Date:   Tue Apr 2 19:58:37 2013 +0800
[4.8] Use READELF_FOR_TARGET in GCC 4.8

See
  b159d4300781ae367096e05076df56b1467d0d9b
  4ecf441b08bb3f039e3836b7517f079be70583ad
  651152db0b741de25918b21c42d604b8b6564eaa
  3c138513fb44386c87bd5276725d5459f9243833

Change-Id: I6a76c29b0cca118dba4ae012ef053a872f461da1

Author: Andrew Hsieh <andrewhsieh@google.com>
Date:   Tue Apr 2 20:02:05 2013 +0800
[4.8] GNU libstdc++ --enable-linux-futex

See fe1a20404b19d5dd0cd0988d080cff8a455c2a76

Change-Id: I93f281d919bce84796670dc1b29917c690d39c15

Author: Andrew Hsieh <andrewhsieh@google.com>
Date:   Tue Apr 2 20:29:20 2013 +0800