AArch64: add atomic support parameters to TargetInfo

This allows Clang to detect and deal wih __atomic_* operations properly on
AArch64. Previously we produced an error when encountering them at high
optimisation levels.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175438 91177308-0d34-0410-b5e6-96231b3b80d8
Correctly determine */& usage in more cases.

This fixes llvm.org/PR15248.

Before:
Test::Test(int b) : a(b *b) {}
for (int i = 0; i < a *a; ++i) {}

After:
Test::Test(int b) : a(b * b) {}
for (int i = 0; i < a * a; ++i) {}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175439 91177308-0d34-0410-b5e6-96231b3b80d8