[llvm-mca] Use a different character to flag instructions with side-effects in the...

[llvm-mca] Use a different character to flag instructions with side-effects in the Instruction Info View. NFC

This makes easier to identify changes in the instruction info flags.  It also
helps spotting potential regressions similar to the one recently introduced at
r336728.

Using the same character to mark MayLoad/MayStore/HasSideEffects is problematic
for llvm-lit. When pattern matching substrings, llvm-lit consumes tabs and
spaces. A change in position of the flag marker may not trigger a test failure.

This patch only changes the character used for flag `hasSideEffects`. The reason
why I didn't touch other flags is because I want to avoid spamming the mailing
because of the massive diff due to the numerous tests affected by this change.

In future, each instruction flag should be associated with a different character
in the Instruction Info View.

llvm-svn: 336797