Revise supported-options.nostack

The phrase "for a function call at the start..." creates a miscue. One would tend to read "at the start" as restricting the kind of function call until realizing that doesn't make sense in this context; then one has to backtrack. Let's move that clause earlier to avoid this. Should some of these be nonrestrictive clauses? Are they parenthetical? We'll say "no" for now, but arguably this could go the other way.

Author: traviscross

src/inline-assembly.md

@@ -1226,7 +1226,7 @@ let _: () = unsafe {
 
 r[asm.options.supported-options.nostack]
 - `nostack`: The assembly code does not push data to the stack, or write to the stack red-zone (if supported by the target).
- If this option is *not* used then the stack pointer is guaranteed by the compiler to be suitably aligned (according to the target ABI) for a function call at the start of the assembly code.
+ If this option is *not* used then the stack pointer is guaranteed by the compiler at the start of the assembly code to be suitably aligned (according to the target ABI) for a function call.
 
 <!-- no_run: Test has undefined behavior at runtime -->
 ```rust,no_run