* stage1 backend allows configuring the uwtables function attr
   via a flag rather than its own logic.
 * stage2 defaults to enabling uwtable attr when
   linking libunwind, or always on windows
 * stage2 makes link_eh_frame_hdr true automatically if uwtable
   attr is set to be on for zig functions
 * CLI: add -funwind-tables and -fno-unwind-tables to allow the user to
   override the defaults.
 * hook it up to `zig cc`

closes #9046