[libc][stdfix] Generate stdfix.h header with fixed point precision macros...

[libc][stdfix] Generate stdfix.h header with fixed point precision macros according to ISO/IEC TR 18037:2008 standard, and add fixed point type support detection. (#81255)

Fixed point extension standard:
https://standards.iso.org/ittf/PubliclyAvailableStandards/c051126_ISO_IEC_TR_18037_2008.zip