runtime: disable memory profiler in gc_test
runtime: disable memory profiler in gc_test

This lets the test pass on PPC64 GNU/Linux, which uses a much
larger page size and thus uses more memory to hold blocks
allocated for memory profiling.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/6048054

bryanxu/go-zh,rflanagan/reginaldflanagan-project1,d0f/go-zh,webfd/go-zh,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,d0f/go-zh,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,Triskite/willstone-goclone,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,Triskite/willstone-goclone,scirelli/scirelli-go,mhennings/marcohennings-go,d0f/go-zh,mhennings/marcohennings-go,d0f/go-zh,rdp/rogerpack2005-golang,Triskite/willstone-goclone,mhennings/marcohennings-go,Triskite/willstone-goclone,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,bryanxu/go-zh,scirelli/scirelli-go,rflanagan/reginaldflanagan-project1,d0f/go-zh,Triskite/willstone-goclone,bryanxu/go-zh,Triskite/willstone-goclone,bryanxu/go-zh,Triskite/willstone-goclone,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,Triskite/willstone-goclone,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,d0f/go-zh,mhennings/marcohennings-go,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,d0f/go-zh,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,bryanxu/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,webfd/go-zh,scirelli/scirelli-go,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,webfd/go-zh,webfd/go-zh,scirelli/scirelli-go,rdp/rogerpack2005-golang,bryanxu/go-zh,rdp/rogerpack2005-golang,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,d0f/go-zh,bryanxu/go-zh,mhennings/marcohennings-go,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,webfd/go-zh,scirelli/scirelli-go,webfd/go-zh,rdp/rogerpack2005-golang,scirelli/scirelli-go