[PATCH] RISC-V: Implment H modifier for printing the next register name

[PATCH] RISC-V: Implment H modifier for printing the next register name

For RV32 inline assembly, when handling 64-bit integer data, it is
often necessary to process the lower and upper 32 bits separately.
Unfortunately, we can only output the current register name
(lower 32 bits) but not the next register name (upper 32 bits).

To address this, the modifier 'H' has been added to allow users
to handle the upper 32 bits of the data. While I believe the
modifier 'N' (representing the next register name) might be more
suitable for this functionality, 'N' is already in use.
Therefore, 'H' (representing the high register) was chosen instead.

Co-Authored-By: Dimitar Dimitrov <dimitar@dinux.eu>
gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_print_operand): Add H.
	* doc/extend.texi: Document for H.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/modifier-H-error-1.c: New test.
	* gcc.target/riscv/modifier-H-error-2.c: New test.
	* gcc.target/riscv/modifier-H.c: New test.