os: implement os.Chtimes

[achille-roussel]

Opening this PR as a draft because I'm running into an issue that someone more familiar with the TinyGo build may be more equipped to solve.

utimes in wasi-libc has a dependency on __builtin_mul_overflow via https://github.com/WebAssembly/wasi-libc/blob/3189cd1ceec8771e8f27faab58ad05d4d6c369ef/libc-bottom-half/cloudlibc/src/common/time.h, which gets translated by LLVM to a call to __muloti4 from compiler-rt, which isn't being linked to tinygo.

$ ./build/tinygo test -target=wasi os
tinygo:wasm-ld: error: /home/achille_roussel/go/src/github.com/achille-roussel/tinygo/lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a(utimensat.o): undefined symbol: __muloti4
tinygo:wasm-ld: error: /home/achille_roussel/go/src/github.com/achille-roussel/tinygo/lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a(utimensat.o): undefined symbol: __muloti4
failed to run tool: wasm-ld
FAIL	os	0.000s
error: failed to link /tmp/tinygo1517931148/main: exit status 1

[dgryski]

Almost certainly #3501

[achille-roussel]

I'm going to close this PR since tinygo has integrated the Go 1.21 changes where os.(*File).Chtimes is implemented.