[lsan] Fix r182256.

Add missing call to GetUserBegin().

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@182267 91177308-0d34-0410-b5e6-96231b3b80d8
Build LSan on x86_64 only if this target is supported

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@182272 91177308-0d34-0410-b5e6-96231b3b80d8
[nolibc] Make GetArgsAndEnv libc-independent.

__libc_stack_end is made into a weak symbol if possible.  If libc is
not linked, read args and environment from /proc.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@182276 91177308-0d34-0410-b5e6-96231b3b80d8