Change Details

This adds an option equivalent to configure's `--with-asm=arm`. It is mutually exclusive with the x86_64 assembly, so the `SECP256K1_USE_ASM` is renamed to `SECP256K1_USE_X86_64_ASM` for clarity and an error message is displayed as needed.

This adds an option equivalent to configure's `--with-asm=arm`. It is mutually exclusive with the x86_64 assembly, so the `SECP256K1_USE_ASM` can now be set to `x86_64` or `ARM` or any other value to disable ASM completely.

This adds an option equivalent to configure's `--with-asm=arm`. It is mutually exclusive with the x86_64 assembly, so the `SECP256K1_USE_ASM` is renamed to `SECP256K1_USE_Xcan now be set to `x86_64_ASM` for clarity` or `ARM` or and an error message isany other value to displayed as neededable ASM completely.