prevent an llvm developer from mistakenly thinking that just because the
intrinsic has volatile flags that volatile operations can be converted
to or folded into them.

Platforms may rely on volatile loads and stores of natively supported
data width to be executed as single instruction. When compiling
C, this expectation likely holds for l-values of volatile primitive
types with native hardware support, but not necessarily for aggregate
types. The frontend upholds these expectations, which are not
specified in the IR.

llvm-svn: 173974