SWIG: Ensure ptrdiff_t is a known type in gcc >= 4.6.1
SWIG: Ensure ptrdiff_t is a known type in gcc >= 4.6.1

This patch fixes a compilation error that occurs with gcc >= 4.6.1,
caused by swig not including cstddef and not using the std:: namespace
prefix for ptrdiff_t. There is an old patch,
http://reviews.m5sim.org/r/913/ that no longer applies cleanly and
this might be re-iterating the same issue.

We work around the problem by always enforcing the inclusion of
cstddef in all swig interface declarations, and also by explicitly
using std::ptrdiff_t.

austinharris/gem5-riscv,powerjg/gem5-ci-test,rallylee/gem5,joerocklin/gem5,aclifton/cpeg853-gem5,powerjg/gem5-ci-test,qizenguf/MLC-STT,gem5/gem5,SanchayanMaity/gem5,austinharris/gem5-riscv,SanchayanMaity/gem5,powerjg/gem5-ci-test,KuroeKurose/gem5,powerjg/gem5-ci-test,SanchayanMaity/gem5,joerocklin/gem5,rjschof/gem5,austinharris/gem5-riscv,aclifton/cpeg853-gem5,austinharris/gem5-riscv,aclifton/cpeg853-gem5,briancoutinho0905/2dsampling,Weil0ng/gem5,markoshorro/gem5,samueldotj/TeeRISC-Simulator,joerocklin/gem5,yb-kim/gemV,powerjg/gem5-ci-test,samueldotj/TeeRISC-Simulator,Weil0ng/gem5,samueldotj/TeeRISC-Simulator,gem5/gem5,aclifton/cpeg853-gem5,rjschof/gem5,markoshorro/gem5,markoshorro/gem5,sobercoder/gem5,cancro7/gem5,gem5/gem5,SanchayanMaity/gem5,KuroeKurose/gem5,zlfben/gem5,markoshorro/gem5,aclifton/cpeg853-gem5,gedare/gem5,joerocklin/gem5,zlfben/gem5,rallylee/gem5,HwisooSo/gemV-update,zlfben/gem5,gedare/gem5,austinharris/gem5-riscv,yb-kim/gemV,gedare/gem5,sobercoder/gem5,HwisooSo/gemV-update,Weil0ng/gem5,zlfben/gem5,briancoutinho0905/2dsampling,rallylee/gem5,rallylee/gem5,samueldotj/TeeRISC-Simulator,cancro7/gem5,gedare/gem5,briancoutinho0905/2dsampling,kaiyuanl/gem5,gedare/gem5,Weil0ng/gem5,samueldotj/TeeRISC-Simulator,samueldotj/TeeRISC-Simulator,powerjg/gem5-ci-test,rjschof/gem5,sobercoder/gem5,TUD-OS/gem5-dtu,austinharris/gem5-riscv,SanchayanMaity/gem5,rallylee/gem5,Weil0ng/gem5,zlfben/gem5,briancoutinho0905/2dsampling,yb-kim/gemV,cancro7/gem5,aclifton/cpeg853-gem5,rallylee/gem5,HwisooSo/gemV-update,rjschof/gem5,KuroeKurose/gem5,sobercoder/gem5,Weil0ng/gem5,gedare/gem5,cancro7/gem5,samueldotj/TeeRISC-Simulator,yb-kim/gemV,cancro7/gem5,qizenguf/MLC-STT,joerocklin/gem5,joerocklin/gem5,HwisooSo/gemV-update,gem5/gem5,yb-kim/gemV,kaiyuanl/gem5,gem5/gem5,kaiyuanl/gem5,gem5/gem5,sobercoder/gem5,sobercoder/gem5,SanchayanMaity/gem5,cancro7/gem5,rjschof/gem5,markoshorro/gem5,briancoutinho0905/2dsampling,TUD-OS/gem5-dtu,qizenguf/MLC-STT,sobercoder/gem5,Weil0ng/gem5,yb-kim/gemV,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,qizenguf/MLC-STT,rallylee/gem5,SanchayanMaity/gem5,briancoutinho0905/2dsampling,rjschof/gem5,markoshorro/gem5,TUD-OS/gem5-dtu,yb-kim/gemV,joerocklin/gem5,joerocklin/gem5,rjschof/gem5,aclifton/cpeg853-gem5,austinharris/gem5-riscv,qizenguf/MLC-STT,gedare/gem5,kaiyuanl/gem5,cancro7/gem5,qizenguf/MLC-STT,KuroeKurose/gem5,KuroeKurose/gem5,powerjg/gem5-ci-test,gem5/gem5,kaiyuanl/gem5,kaiyuanl/gem5,HwisooSo/gemV-update,yb-kim/gemV,HwisooSo/gemV-update,kaiyuanl/gem5,zlfben/gem5,KuroeKurose/gem5,briancoutinho0905/2dsampling,zlfben/gem5,TUD-OS/gem5-dtu,qizenguf/MLC-STT,KuroeKurose/gem5,TUD-OS/gem5-dtu,HwisooSo/gemV-update,markoshorro/gem5