build(native): exclude daemon-only sources from libsentry.so

[jpnurmi]

Move the client-side launcher from the daemon to the backend, and stop building daemon-only crash processing, minidump writers, and remote unwinding into libsentry.so.

sentry-crash previously copied all sources from the sentry target, so daemon-only crash processing, minidump, and remote unwinding sources were also built into libsentry.so. Add those sources directly to sentry-crash instead. Keep daemon_start in the native backend because launching the handler remains a client-side responsibility.

This slices off ~9% from libsentry.so ^[1], and removes the following large stack frames:

• sentry__write_minidump: 1,216,336 bytes
• sentry__process_crash: 18,368 bytes
• enrich_frame_with_symbol: 14,592 bytes
• write_attachment_to_envelope: 8,448 bytes

Note: the source split does not preclude a potential future in-process mode.

Before vs. after

Before (Linux x86_64)

• libsentry.so: 2.7MiB
• sentry-crash: 3.4MiB

Stack frame	Size (bytes)
sentry__write_minidump	1,216,336
sentry__process_crash	18,368
enrich_frame_with_symbol	14,592
sentry__crash_daemon_start	8,528
write_attachment_to_envelope.isra	8,448
crash_signal_handler	6,336
native_backend_shutdown	5,184
elf_locate_symtab	4,400
sentry__crash_daemon_main	4,256
find_mem_range_from_fd	4,192
sentry__path_absolute	4,128
sentry__path_current_exe	4,128
sentry__crash_handler_init	2,224
ensure_installed	2,208
sentry_value_new_stacktrace	2,160
sentry__unwind_stack_libunwind	2,128
write_thread_context	1,792
ptrace_capture_thread.isra	1,296
build_stacktrace_for_thread	1,216
handler	1,088

After (Linux x86_64)

• libsentry.so: 2.5MiB
• sentry-crash: 3.4MiB

Stack frame	Size (bytes)
daemon_start	8,528
crash_signal_handler	6,336
native_backend_shutdown	5,184
find_mem_range_from_fd	4,192
sentry__path_absolute	4,128
sentry__path_current_exe	4,128
sentry__crash_handler_init	2,224
ensure_installed	2,208
sentry_value_new_stacktrace	2,160
sentry__unwind_stack_libunwind	2,128
handler	1,088

Commands for reference:

# lib size
cmake -S . -B build -DSENTRY_BACKEND=native -DCMAKE_BUILD_TYPE=Release && cmake --build build --target sentry --target sentry-crash --parallel && stat -c '%s %n' build/libsentry.so build/sentry-crash | numfmt --field=1 --to=iec-i --suffix=B

# stack usage
cmake -S . -B build-stack -DSENTRY_BACKEND=native -DCMAKE_C_FLAGS=-fstack-usage -DCMAKE_CXX_FLAGS=-fstack-usage && cmake --build build-stack --target sentry && find build-stack -path '*/CMakeFiles/sentry.dir/*.su'   -exec awk -F '\t' '{
    fn = $1
    sub(/^.*:[0-9]+:[0-9]+:/, "", fn)
    print $2, fn
  }' {} + |   sort -k1,1nr -k2,2 | head -n 20

^{[1] 55kb/622kb in Release mode / 252kb/2.7mb in ReleaseWithDbg on Linux x86_64}

[codecov]

Codecov Report

❌ Patch coverage is 57.72358% with 52 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.34%. Comparing base (719803e) to head (736b4ea).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2031      +/-   ##
==========================================
+ Coverage   74.21%   74.34%   +0.12%     
==========================================
  Files         104      104              
  Lines       26627    26623       -4     
  Branches     4844     4844              
==========================================
+ Hits        19762    19793      +31     
+ Misses       5519     5491      -28     
+ Partials     1346     1339       -7     

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