Fix PR77489 -- mangling of discriminator >= 1

Fix PR77489 -- mangling of discriminator >= 1

libiberty:

	PR c++/77489
	* cp-demangle.c (d_discriminator): Handle discriminator >= 10.
	* testsuite/demangle-expected: Add tests for discriminator.

gcc:
	PR c++/77489
	* doc/invoke.texi (fabi-version): Document discriminator mangling.

gcc/cp:

	PR c++/77489
	* mangle.c (write_discriminator): Handle discriminator >= 10.

From-SVN: r244566