RISC-V: Add Zalrsc and Zaamo testsuite support

RISC-V: Add Zalrsc and Zaamo testsuite support

Convert testsuite infrastructure to use Zalrsc and Zaamo rather than A.

gcc/ChangeLog:

	* doc/sourcebuild.texi: Add docs for atomic extension testsuite infra.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/amo-table-a-6-amo-add-1.c: Use Zaamo rather than A.
	* gcc.target/riscv/amo-table-a-6-amo-add-2.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-amo-add-3.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-amo-add-4.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-amo-add-5.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-compare-exchange-1.c: Use Zalrsc rather
	than A.
	* gcc.target/riscv/amo-table-a-6-compare-exchange-2.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-compare-exchange-3.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-compare-exchange-4.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-compare-exchange-5.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-compare-exchange-6.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-compare-exchange-7.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-subword-amo-add-1.c: Use Zaamo rather
	than A.
	* gcc.target/riscv/amo-table-a-6-subword-amo-add-2.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-subword-amo-add-3.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-subword-amo-add-4.c: Ditto.
	* gcc.target/riscv/amo-table-a-6-subword-amo-add-5.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-amo-add-1.c: Add Zaamo option.
	* gcc.target/riscv/amo-table-ztso-amo-add-2.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-amo-add-3.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-amo-add-4.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-amo-add-5.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-1.c: Use Zalrsc rather
	than A.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-2.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-3.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-4.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-5.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-6.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-7.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-1.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-2.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-3.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-4.c: Ditto.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-5.c: Ditto.
	* lib/target-supports.exp: Add testsuite infrastructure support for
	Zaamo and Zalrsc.

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>