Using a `--section-start` address in the test was causing link errors on
some targets. Now it uses a linker script to move the note after `.bss`,
which should still have the kind of memory offset we're looking for.
This is a follow-up to #114907 to fix buildbot errors.
This function is always examining its own ELF headers in memory, but it
was trying to use conditions between examining files or memory, and it
wasn't accounting for LOAD offsets at runtime. This is especially bad if
a loaded segment has additional padding that's not in the file offsets.
Now we do a first scan of the program headers to figure out the runtime
base address based on `PT_PHDR` and/or `PT_DYNAMIC` (else assume zero),
similar to libc's `do_start`. Then each `PT_NOTE` pointer is simply the
base plus the segments's `pt_vaddr`, which includes LOAD offsets.
Fixes#114605
