Enable the asm interpreter on Windows for both x86_64 and ARM64. The
x86_64 backend now emits COFF assembly using the Win64 ABI. It handles
argument registers, non-volatile register saves, shadow space, SEH
unwind directives, and raw-native sret lowering. Its epilogue is left
as normal x64 instructions instead of ARM64-style SEH epilogue
directives, which older ClangCL assemblers reject.
The AArch64 backend now emits Windows ARM64 COFF assembly as well,
including COFF relocations, .rdata dispatch tables, SEH unwind metadata,
frame sizing, handler alignment rules, and raw-native sret lowering.
CMake selects COFF for Windows asmint output and enables generation for
both Windows architectures.
AsmIntGen coverage checks the Windows x64 epilogue output and the ARM64
COFF unwind output. test-js and test262 have no regressions with asmint
enabled compared with the C++ interpreter.
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