ci: use thin LTO for the armv7 sciter build

The nightly armv7 sciter build aborts while compiling the final `rustdesk`
binary:

    fatal runtime error: Rust cannot catch foreign exceptions
    error: could not compile `rustdesk` (bin "rustdesk")  (signal: 6, SIGABRT)

armv7 is the only 32-bit target in this job that links the whole binary, and
`[profile.release]` uses fat LTO with codegen-units = 1, so LLVM merges every
module into a single unit and runs past the ~3GB address space a 32-bit
process gets. The allocation failure surfaces as a C++ bad_alloc unwinding
into rustc's Rust frames, which is what that "foreign exceptions" abort is.
The x86_64 sciter build uses the same settings and passes, as do aarch64 and
every other 64-bit job in the same run, so this is specific to the 32-bit
address space rather than to the source change itself.

It started failing once the crate graph grew (hbb_common is pulled with the
`webrtc` feature unconditionally), which pushed an already marginal target
over the limit.

Use thin LTO with more codegen units for armv7 only. Peak memory stays
bounded while cross-crate inlining is kept, and 64-bit targets are untouched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lq6xFoeEmjcuKwRx1GfdQ2

.github/workflows/flutter-build.yml

@@ -2300,6 +2300,16 @@ jobs:
             # build rustdesk
             python3 ./res/inline-sciter.py
             export CARGO_INCREMENTAL=0
+            # armv7 is the only 32-bit target in this job that links the whole binary, and the
+            # release profile uses fat LTO with codegen-units=1. LLVM then merges every module
+            # into a single unit and runs past the ~3GB address space a 32-bit process gets,
+            # aborting rustc with "Rust cannot catch foreign exceptions" (a C++ bad_alloc from
+            # LLVM unwinding into rustc's Rust frames). Thin LTO keeps peak memory bounded and
+            # still allows cross-crate inlining; 64-bit targets keep fat LTO untouched.
+            if [ "${{ matrix.job.arch }}" = "armv7" ]; then
+              export CARGO_PROFILE_RELEASE_LTO=thin
+              export CARGO_PROFILE_RELEASE_CODEGEN_UNITS=16
+            fi
             cargo build --locked --features inline${{ matrix.job.extra_features }} --release --bins --jobs 1
             # make debian package
             mkdir -p ./Release