gas: BPF pseudo-c syntax tests

This patch expands the GAS BPF testsuite in order to also test the
alternative pseudo-C syntax used in BPF assembly.

This includes three main changes:

- Some general GAS tests involving assignment and equality operands in
  expressions (such as = and ==) are disabled in bpf-* targets,
  because the syntax collides with the pseudo-C BPF assembly syntax.

- New tests are added to the BPF GAS testsuite that test the pseudo-c
syntax.  Tests for all BPF instructions are included.

- New tests are added to the BPF GAS testsuite that test the support
  for both syntaxes in the same source.

gas/ChangeLog:

2023-04-20  Guillermo E. Martinez  <guillermo.e.martinez@oracle.com>

	PR gas/29728
	* testsuite/gas/all/assign-bad-recursive.d: Skip test in bpf-*
	targets.
	* testsuite/gas/all/eqv-dot.d: Likewise.
	* testsuite/gas/all/gas.exp: Skip other assignment tests in bpf-*.
	* testsuite/gas/bpf/alu-pseudoc.s: New file.
	* testsuite/gas/bpf/pseudoc-normal.s: Likewise.
	* testsuite/gas/bpf/pseudoc-normal.d: Likewise.
	* testsuite/gas/bpf/pseudoc-normal-be.d: Likewise.
	* testsuite/gas/bpf/mem-pseudoc.s: Likewise.
	* testsuite/gas/bpf/lddw-pseudoc.s: Likewise.
	* testsuite/gas/bpf/jump32-pseudoc.s: Likewise.
	* testsuite/gas/bpf/jump-pseudoc.s: Likewise.
	* testsuite/gas/bpf/indcall-1-pseudoc.s: Likewise.
	* testsuite/gas/bpf/atomic-pseudoc.s: Likewise.
	* testsuite/gas/bpf/alu32-pseudoc.s: Likewise.
	* testsuite/gas/bpf/*.d: Add -pseudoc variants of the tests.