x86_64: PR target/100711: Splitters for pandn

x86_64: PR target/100711: Splitters for pandn

This patch addresses PR target/100711 by introducing define_split
patterns so that not/broadcast/pand may be simplified (by combine)
to broadcast/pandn.  This introduces two splitters one for optimizing
pandn on TARGET_SSE for V4SI and V2DI, and another for vpandn on
TARGET_AVX2 for V16QI, V8HI, V32QI, V16HI and V8SI.  Each splitter
has its own new testcase.

I've also confirmed that not/broadcast/pandn is already getting
simplified to broadcast/pand by the middle-end optimizers.

2021-11-30  Roger Sayle  <roger@nextmovesoftware.com>
	    Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog
	PR target/100711
	* config/i386/sse.md (define_split): New splitters to simplify
	not;vec_duplicate;and as vec_duplicate;andn.

gcc/testsuite/ChangeLog
	PR target/100711
	* gcc.target/i386/pr100711-1.c: New test case.
	* gcc.target/i386/pr100711-2.c: New test case.