[inline asm] Implement mayLoad and mayStore for inline assembly. In general,

[inline asm] Implement mayLoad and mayStore for inline assembly.  In general,
the MachineInstr MayLoad/MayLoad flags are based on the tablegen implementation.
For inline assembly, however, we need to compute these based on the constraints.

Revert r166929 as this is no longer needed, but leave the test case in place.
rdar://12033048 and PR13504

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167040 91177308-0d34-0410-b5e6-96231b3b80d8