X86: Allow the stack probe size to be configurable per function

LLVM emits stack probes on Windows targets to ensure that the stack is
correctly accessed.  However, the amount of stack allocated before
emitting such a probe is hardcoded to 4096.

It is desirable to have this be configurable so that a function might
opt-out of stack probes.  Our level of granularity is at the function
level instead of, say, the module level to permit proper generation of
code after LTO.

Patch by Andrew H!

N.B.  The inliner needs to be updated to properly consider what happens
after inlining a function with a specific stack-probe-size into another
function with a different stack-probe-size.

llvm-svn: 225360