xtensa: Make use of BALL/BNALL instructions

xtensa: Make use of BALL/BNALL instructions

In Xtensa ISA, there is no single machine instruction that calculates unary
bitwise negation, but a few similar fused instructions are exist:

  "BALL  Ax, Ay, label"  // if ((~Ax & Ay) == 0) goto label;
  "BNALL Ax, Ay, label"  // if ((~Ax & Ay) != 0) goto label;

These instructions have never been emitted before, but it seems no reason not
to make use of them.

gcc/ChangeLog:

	* config/xtensa/xtensa.md (*masktrue_bitcmpl): New insn pattern.

gcc/testsuite/ChangeLog:

	* gcc.target/xtensa/BALL-BNALL.c: New.