[NFC][X86][AArch64] Shift amount masking: tests that show that 'neg' doesn't last

Meaning if we were to produce 'neg' in dagcombine, we will get an
endless cycle; some inverse transform would need to be guarded somehow.

Also, the 'and (sub 0, x), 31' variant is sticky,
doesn't get optimized in any way.

https://bugs.llvm.org/show_bug.cgi?id=41952

llvm-svn: 361254