[gem5] Fix bug in SConstruct to enable compilation with clang.
[gem5] Fix bug in SConstruct to enable compilation with clang.

basicthinker/Sexain-MemController,basicthinker/Sexain-MemController,basicthinker/Sexain-MemController,basicthinker/Sexain-MemController,basicthinker/Sexain-MemController,basicthinker/Sexain-MemController,basicthinker/Sexain-MemController,basicthinker/Sexain-MemController