Let the assembler emit an .eh_frame for the trampoline, matching the
frame layout jit_unwind.c describes.

…ssembly

Extract the .eh_frame the assembler emits for the trampoline object at
build time into trampoline_ehframe.h and patch only the FDE address
fields at runtime. Building with the perf trampoline now needs a host
Python, and configure disables the trampoline with a warning when none
is usable.

Check the FDEs in jitdump files against their code load records, cover
the generator's parsers, and validate the header structure from C.

Objects including it did not rebuild when the header changed.

_bootstrap_python cannot load shared extension modules such as _struct. Read the ELF and Mach-O fields with int.from_bytes and reject reads past the end of the file.

…ython

Emit the trampoline's .eh_frame as a C file linked like Python/frozen.o, outside the objects the bootstrap programs link, which define an empty stub instead. A default build no longer needs a host Python for the perf trampoline, so configure stops probing for one.