[LTT] mark the CFI jumptable naked on Windows (#170371)
We were not marking the `.cfi.jumptable` functions as `naked` on windows. The referenced bug (https://llvm.org/bugs/show_bug.cgi?id=28641#c3) appears to be fixed:
```bash
build/bin/opt -S -passes=lowertypetests -mtriple=i686-pc-win32 llvm/test/Transforms/LowerTypeTests/function.ll | build/bin/llc -O0
```
```
L_.cfi.jumptable: # @.cfi.jumptable
# %bb.0: # %entry
#APP
jmp _f.cfi@PLT
int3
int3
int3
#NO_APP
#APP
jmp _g.cfi@PLT
int3
int3
int3
#NO_APP
# -- End function
.section .rdata,"dr"
.p2align 4, 0x0 # @0
```
Not seeing the spilled registers described in the bug anymore.
