tsan: fix freebsd build
freebsd does not have /proc/self/environ



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@211417 91177308-0d34-0410-b5e6-96231b3b80d8
tsan: port to freebsd


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@211418 91177308-0d34-0410-b5e6-96231b3b80d8