Add missing -m64 arguments to makefile
Add missing -m64 arguments to makefile

Before this change, doing "make test" on a 32-bit system fails when
building the tests rather than when running them, with the unexpected
error:

/usr/bin/ld: i386 architecture of input file `allocator.o64' is
incompatible with i386:x86-64 output

Review URL: http://codereview.chromium.org/3342008
aman-iitj/seccompsandbox,marylinh/seccompsandbox,aman-iitj/seccompsandbox,marylinh/seccompsandbox,dj091111/seccompsandbox,dj091111/seccompsandbox,aman-iitj/seccompsandbox,dj091111/seccompsandbox,marylinh/seccompsandbox