mingw-w64-v8: add v8_enable_sandbox=false to build flags

[Copilot]

• Add v8_enable_sandbox=false to the GN build flags in mingw-w64-v8/PKGBUILD
• Fix linker error undefined reference to v8::base::SysInfo::NumberOfProcessors() by restoring --start-group/--end-group around the RSP file in the MinGW toolchain patch

[jeroen]

@copilot can you inspect the CI results and resolve the error?

[Copilot]

@copilot can you inspect the CI results and resolve the error?

The CI was failing with undefined reference to v8::base::SysInfo::NumberOfProcessors() when linking mksnapshot.exe.

The root cause: with v8_enable_sandbox=false, the library ordering in the linker RSP file changes so that libv8_libbase.a (which defines SysInfo::NumberOfProcessors()) ends up positioned before libv8_libplatform.a in the link command. Since the MinGW toolchain patch had removed --start-group/--end-group wrapping from the RSP file, the linker couldn't re-scan libv8_libbase.a to resolve the symbol needed by libv8_libplatform.a.

Fixed in ba707f5 by restoring -Wl,--start-group @"$rspfile" -Wl,--end-group in the MinGW toolchain patch's executable link command, allowing the linker to make multiple passes over the static archives.