[PATCH] Fix getting environment variables for sanitizers needs on FreeBSD

[Ed Maste]

> But where does "extern char **environ" came from? Doesn't it come from libc?

char **environ is provided by crt1 - it's here on FreeBSD -HEAD:
http://svnweb.freebsd.org/base/head/lib/csu/common/ignore_init.c?revision=245133&view=markup

http://reviews.llvm.org/D4229