libgcc: Generated tables for _BitInt <-> _Decimal* conversions [PR102989]

libgcc: Generated tables for _BitInt <-> _Decimal* conversions [PR102989]

The following patch adds a header with generated helper tables to support
computation of powers of 10 from 10^0 to 10^6111 inclusive into a
sufficiently large array of _BitInt limbs.  This is split from the rest
of the libgcc _BitInt support because it is quite large and together it
would run into gcc-patches mail length limits.

2023-09-06  Jakub Jelinek  <jakub@redhat.com>

	PR c/102989
libgcc/
	* soft-fp/bitintpow10.h: New file.