inline-asm: Fix ICE with bitfields in "m" operands [PR100785]

inline-asm: Fix ICE with bitfields in "m" operands [PR100785]

Bitfields, while they live in memory, aren't something inline-asm can easily
operate on.
For C and "=m" or "+m", we were diagnosing bitfields in the past in the
FE, where c_mark_addressable had:
      case COMPONENT_REF:
        if (DECL_C_BIT_FIELD (TREE_OPERAND (x, 1)))
          {
            error
              ("cannot take address of bit-field %qD", TREE_OPERAND (x, 1));
            return false;
          }
but that check got moved in GCC 6 to build_unary_op instead and now we
emit an error during expansion and ICE afterwards (i.e. error-recovery).
For "m" it used to be diagnosed in c_mark_addressable too, but since
GCC 6 it is ice-on-invalid.
For C++, this was never diagnosed in the FE, but used to be diagnosed
in the gimplifier and/or during expansion before 4.8.

The following patch does multiple things:
1) diagnoses it in the FEs
2) stops emitting a redundant diagnostic in the gimplifier using the
   usual way, if we already see error_mark_node, we assume error has
   been emitted already and only diagnose if it wasn't error_mark_node;
   this helps diagnosing the same bug with multiple different
   errors
3) simplifies during expansion the inline asm if any errors have been
   reported (similarly how e.g. vregs pass if it detects errors on
   inline-asm either deletes them or simplifies to bare minimum -
   just labels), so that we don't have error-recovery ICEs there

2021-06-11  Jakub Jelinek  <jakub@redhat.com>

	PR inline-asm/100785
gcc/
	* gimplify.c (gimplify_asm_expr): Don't diagnose errors if
	output or input operands were already error_mark_node.
	* cfgexpand.c (expand_asm_stmt): If errors are emitted,
	remove all inputs, outputs and clobbers from the asm and
	set template to "".
gcc/c/
	* c-typeck.c (c_mark_addressable): Diagnose trying to make
	bit-fields addressable.
gcc/cp/
	* typeck.c (cxx_mark_addressable): Diagnose trying to make
	bit-fields addressable.
gcc/testsuite/
	* c-c++-common/pr100785.c: New test.
	* gcc.dg/pr48552-1.c: Don't expect invalid lvalue errors.
	* gcc.dg/pr48552-2.c: Likewise.