[libc-commits] [libc] [libc] Add getc, ungetc, fflush to enable libc++ iostream on baremetal (PR #175530)

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zeroomega wrote:

We did some investigate on Windows and we believe the reason is that the argument lists sent to the libc hdrgen is too long. See the bat file in question in gist: https://gist.github.com/zeroomega/2e38832bba88e52756dfdd39d9ba7c72

After this patch, additional `--entry-point` arguments makes the total length of the argument to reach 16KiB. Windows has a 32KiB argument list buffer but due to using WCHAR, the effective limit is 16KiB. It causes the cmd.exe fail to parse the bat file generated by the cmake to call the hdrgen and eventually lead to the failure.

The solution would be adding response file support to the libc hdrgen so we don't have to send 16KiB arguments through the command line.

https://github.com/llvm/llvm-project/pull/175530