Port string.startswith() to native code

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extra : rebase_source : 62005750706f932e8542083ad7b05e6d25d3131e
Only write scripts.c if modified by embed action

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extra : rebase_source : 3c8057dd4cad68b32ecc76809baaffcbabce1599
Improve comment filtering in embed action

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extra : rebase_source : 29e09be9b9512a78cc564f3fdd176de177b195e6
Bug: ignores first command line argument after the action
Write scripts.c to right location even when called from a different working directory