[X86] Change the tuning settings for pentium4 to be more modern since its the...

[X86] Change the tuning settings for pentium4 to be more modern since its the default 32-bit cpu in clang

Alternative to D83897. I believe the big change here is that I removed slow unaligned memory 16

Down side that it may adversely effect tuning if someone explicitly targets -march=pentium4 and expects pentium4 tuned code. Of course pentium4 is so old our default behavior with the previous settings may not have been the best either.

Reviewed By: echristo, RKSimon

Differential Revision: https://reviews.llvm.org/D83913