ruby: support EC offset extraction for statically-linked Ruby

[dalehamel]

For statically-linked Ruby binaries (bin/ruby rather than libruby.so), TLS descriptors are not available. Instead, rb_current_ec_noinline accesses the execution context directly via a TP-relative offset (FS:offset on x86_64, MRS tpidr_el0 + ADD on aarch64).

This reuses the asm/amd.ExtractTLSOffset and asm/arm.ExtractTLSOffset infrastructure from the Python TLS PR (open-telemetry#1109) to disassemble rb_current_ec_noinline and extract the offset.

Also changes current_ec_tpbase_tls_offset from u64 to s64 since static TLS offsets (local exec model) are negative on x86_64.

[dalehamel]

Coredump Test Plan

This PR needs a coredump test for a statically-linked Ruby binary (no libruby.so) to exercise the binRubyRegex match and extractEcTLSOffset() disassembly path.

Test: ruby-3.4.7-static-loop (amd64 + arm64)

Build:

ruby-install ruby 3.4.7 -- --disable-shared

Verify the binary is static (no libruby.so):

ldd /opt/rubies/ruby-3.4.7/bin/ruby
# Should show no libruby.so dependency
readelf -s /opt/rubies/ruby-3.4.7/bin/ruby | grep rb_current_ec_noinline
# Should exist — this is the function we disassemble

Capture:

chruby ruby-3.4.7  # the --disable-shared build
ruby tools/coredump/testsources/ruby/loop.rb &
PID=$!
sleep 2
./coredump new -pid $PID -name ruby-3.4.7-static-loop

What this exercises

• binRubyRegex matches bin/ruby instead of libruby*.so
• extractEcTLSOffset() disassembles rb_current_ec_noinline to find the direct TP-relative offset (e.g. FS:0xfffffffffffffff8 on x86_64, MRS tpidr_el0 + ADD #0x38 on aarch64)
• The signed current_ec_tpbase_tls_offset (s64) is used with tsd_base to read ruby_current_ec
• Expected frames should be identical in shape to existing ruby-3.4.x-loop tests

Files to add

• tools/coredump/testdata/amd64/ruby-3.4.7-static-loop.json
• tools/coredump/testdata/arm64/ruby-3.4.7-static-loop.json