bpf: gas: add field overflow checking to the BPF assembler

bpf: gas: add field overflow checking to the BPF assembler

This patch makes the BPF assembler to throughfully check for overflow
in immediates.  This includes relaxed instructions.

Tested in bpf-unknown-none.

gas/ChangeLog:

2023-07-30  Jose E. Marchesi  <jose.marchesi@oracle.com>

	* config/tc-bpf.c (signed_overflow): Copy function from
	tc-aarch64.c.
	(encode_insn): Check for overflow in constant immediates.
	(add_relaxed_insn): Pass relax argument to encode_insn.
	(add_fixed_insn): Likewise.
	* testsuite/gas/bpf/disp16-overflow.d: New file.
	* testsuite/gas/bpf/disp16-overflow.s: Likewise.
	* testsuite/gas/bpf/disp16-overflow.l: Likewise.
	* testsuite/gas/bpf/disp32-overflow.d: Likewise.
	* testsuite/gas/bpf/disp32-overflow.s: Likewise.
	* testsuite/gas/bpf/disp32-overflow.l: Likewise.
	* testsuite/gas/bpf/imm32-overflow.d: Likewise.
	* testsuite/gas/bpf/imm32-overflow.s: Likewise.
	* testsuite/gas/bpf/imm32-overflow.l: Likewise.
	* testsuite/gas/bpf/offset16-overflow.d: Likewise.
	* testsuite/gas/bpf/offset16-overflow.s: Likewise.
	* testsuite/gas/bpf/offset16-overflow.l: Likewise.
	* testsuite/gas/bpf/disp16-overflow-relax.d: Likewise.
	* testsuite/gas/bpf/disp16-overflow-relax.l: Likewise.
	* testsuite/gas/bpf/disp16-overflow-relax.s: Likewise.
	* testsuite/gas/bpf/jump-relax-jump-be.d: New file.
	* testsuite/gas/bpf/bpf.exp: Run new tests.