In llvm-mode, typing a literal '[' would print out '[[', and '(' would
print a '(('. This was a very annoying bug caused by overzealous
syntax-table entries: the parens are already part of the '(' and ')'
class by default. Fix this.
While at it, notice that i32, i64, i1 etc. are not font-locked despite a
clear intent to do so. The issue is that regexp-opt doesn't accept
regular expressions. So, spell out the common literal integers with
different widths.