Add -Zno-jump-tables

This flag mimics GCC/Clang's `-fno-jump-tables` [1][2], which makes
the codegen backend avoid generating jump tables when lowering switches.

In the case of LLVM, the `"no-jump-tables"="true"` function attribute is
added to every function.

The kernel currently needs it for x86 when enabling IBT [3], as well
as for Alpha (plus VDSO objects in MIPS/LoongArch).

[1] https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#index-fno-jump-tables
[2] https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-fjump-tables
[3] https://github.com/torvalds/linux/blob/v6.1/arch/x86/Makefile#L75-L83

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

compiler/rustc_session/src/options.rs

@@ -1421,6 +1421,8 @@ options! {
         "run all passes except codegen; no output"),
     no_generate_arange_section: bool = (false, parse_no_flag, [TRACKED],
         "omit DWARF address ranges that give faster lookups"),
+    no_jump_tables: bool = (false, parse_no_flag, [TRACKED],
+        "disable the jump tables and lookup tables that can be generated from a switch case lowering"),
     no_leak_check: bool = (false, parse_no_flag, [UNTRACKED],
         "disable the 'leak check' for subtyping; unsound, but useful for tests"),
     no_link: bool = (false, parse_no_flag, [TRACKED],