LegalizeDAG: allow libcalls for max/min atomic operations

ARM processors without ldrex/strex need to be able to make libcalls for all
atomic operations, including the newer min/max versions.

The alternative would probably be expanding these operations in terms of
cmpxchg (as x86 does always), but in the configurations where this matters
code-size tends to be paramount so the libcall is more desirable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193398 91177308-0d34-0410-b5e6-96231b3b80d8
ARM: don't expand atomicrmw inline on Cortex-M0

There's a barrier instruction so that should still be used, but most actual
atomic operations are going to need a platform decision on the correct
behaviour (either nop if single-threaded or OS-support otherwise).

rdar://problem/15287210

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193399 91177308-0d34-0410-b5e6-96231b3b80d8
The FIXME was indeed fixed in the linker, comment removed.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193402 91177308-0d34-0410-b5e6-96231b3b80d8
ARM: allow .thumb_func to be separated from symbol definition

When assembling, a .thumb_func directive is supposed to be applicable to the
next symbol definition, even if there are intervening directives. We were
racing ahead to try and find it, and this commit should fix the issue.

Patch by Gabor Ballabas

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193403 91177308-0d34-0410-b5e6-96231b3b80d8