Enable LTO for the is_linux case in BUILD.gn as well.

This patch has been upstream merged into Flutter.
flutter/flutter#176191

…10145)

Manual roll requested by tarrinneal@google.com

flutter/flutter@96fe3b3...c9608e2

2025-09-30 matt.kosarek@canonical.com Implement framework interface for the dialog window archetype (flutter/flutter#176202)
2025-09-30 jhy03261997@gmail.com Update flutter test to use SemanticsFlags (flutter/flutter#175987)
2025-09-30 1063596+reidbaker@users.noreply.github.com Set minimum supported java version to 17  (flutter/flutter#176226)
2025-09-30 mdebbar@google.com Reduce timeout for Linux web_tool_tests back to 60 (flutter/flutter#176286)
2025-09-30 engine-flutter-autoroll@skia.org Roll Packages from 34eec78 to 287739d (9 revisions) (flutter/flutter#176284)
2025-09-30 mdebbar@google.com [web] Bump Firefox to 143.0 (flutter/flutter#176110)
2025-09-30 32538273+ValentinVignal@users.noreply.github.com Migrate to `WidgetStateBorderSide` (flutter/flutter#176164)
2025-09-30 78146827+RootHex200@users.noreply.github.com Enhance input decorator padding logic for character counter in text f… (flutter/flutter#175706)
2025-09-30 jacksongardner@google.com Update the test package for the web engine unit test bits. (flutter/flutter#176241)
2025-09-30 robert.ancell@canonical.com Warn if embedder API calls don't return success (flutter/flutter#176184)
2025-09-30 engine-flutter-autoroll@skia.org Roll Fuchsia Test Scripts from APSBP-sS-3FX69Ihf... to JUeFbA8y0E-_pj-bg... (flutter/flutter#176243)
2025-09-30 jason-simmons@users.noreply.github.com Roll GN to 81b24e01 (flutter/flutter#176119)
2025-09-29 matt.kosarek@canonical.com Rename DisplayMonitor to DisplayManager on Win32 (flutter/flutter#175619)
2025-09-29 mohamed.nayef95@gmail.com [Android] Use headingLevel for heading accessibility property (flutter/flutter#175416)
2025-09-29 80628866+markyang92@users.noreply.github.com BUILD.gn: Support LTO build on Linux (flutter/flutter#176191)
2025-09-29 mohellebiabdessalem@gmail.com fix `assertEquals` arguments are in wrong order in `FlutterJNITest.java` (flutter/flutter#175728)
2025-09-29 mohellebiabdessalem@gmail.com Add tests for `Project` getters  (flutter/flutter#175994)
2025-09-29 engine-flutter-autoroll@skia.org Roll Fuchsia Linux SDK from 8zjcJic_DtvB2Bo2x... to rcOl0yxJb4znJ903Y... (flutter/flutter#176215)
2025-09-29 mohellebiabdessalem@gmail.com Clean up typos in `PlatformViewsControllerTest.java` (flutter/flutter#175725)
2025-09-29 1063596+reidbaker@users.noreply.github.com Migrate java 11 usage to java 17 usage for templates (flutter/flutter#176203)
2025-09-29 aam@google.com User Invoke-Expression instead of call operator for nested Powershell scripts invocations (on Windows) (flutter/flutter#175941)
2025-09-29 jmccandless@google.com Update changelog as on 3.35 branch (flutter/flutter#176216)
2025-09-29 mohellebiabdessalem@gmail.com fix typo in `Crashes.md` (flutter/flutter#175959)
2025-09-29 15619084+vashworth@users.noreply.github.com Add scene plugin lifecycle events (flutter/flutter#175866)
2025-09-29 1063596+reidbaker@users.noreply.github.com Migrate tests and documentation to set java version to 17 (flutter/flutter#176204)
2025-09-29 jessiewong401@gmail.com Update Engine CI to use NDK r28c  (flutter/flutter#175870)

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Add support for LTO builds on Linux.

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---

- Enable LTO on Linux.
- Build test
  - I validated the build in the Yocto build system using meta-flutter

# Build before modification.
```bash
# clone poky
$ source oe-init-build-env
$ echo "MACHINE = \"genericarm64\"" >> build/conf/local.conf

# clone meta-flutter. 
$ git clone https://github.com/meta-flutter/meta-flutter.git
# Added meta-oe and meta-flutter to BBLAYERS in build/conf/bblayers.conf
$ bitbake flutter-engine

# Check whether LTO has been applied in compile_commands.json
$ cat build/tmp/work/armv8a-poky-linux/flutter-engine/3.32.8/sources/gn/engine/src/out/linux_debug_arm64/compile_commands.json | grep "\-flto"

..nothing
```

# Build after modification.
```
# checkout modified meta-flutter  meta-flutter/meta-flutter@a901568
$ cd meta-flutter
$ git remote add markyang92 https://github.com/markyang92/meta-flutter.git
$ git fetch markyang92 a901568da38de2ad3c8a176311b86d8e0f2bb1c1
$ git cherry-pick FETCH_HEAD
$ cd ..

$ bitbake flutter-engine

# Check whether LTO has been applied in compile_commands.json
$ cat build/tmp/work/armv8a-poky-linux/flutter-engine/3.32.8/sources/gn/engine/src/out/linux_debug_arm64/compile_commands.json | grep "\-flto"
    "command": ".....clang++ ... Omitted .. \
 -flto ..... \
-g0 -Wunreachable-code  -fvisibility-inlines-hidden -std=c++17 -fno-rtti -nostdinc++ -nostdinc++ -fvisibility=hidden -fno-exceptions   -c ../../flutter/fml/string_conversion.cc -o  clang_x64/obj/flutter/fml/string_conversion.string_conversion.o"
```