re/reg_mesg.t: Add tests for suppressing warnings

This automatically adds a test for each warning to verify that turning
off the warning category works.
re/reg_mesg.t: White-space only; no code changes
reg_mesg.t: Add cpabilities; improve output

This adds the capability to have tests that each generate multiple
warnings, and it improves the flow so that if a test fails that make
moot subsequent tests, those tests are skipped.
regcomp.c: Change warning category to just deprecated

The warnings for \b{ and \B{ were added in the 5.17 series; they are a
deprecation warning which should be turned off by that category.  One
should not have to turn off regular regexp warnings as well to get rid
of these.
Move t/lib/warnings/regcomp to t/re/reg_mesg.t

reg_mesg.t has better infrastructure to more easily add and maintain
these warnings.
reg_mesg.t: Remove repetitious boiler plate

All the messages have boiler plate that can be removed and inserted by
the subroutine that does insertion anyway.
regen/regcharclass.pl: Add capability

This allows one to generate macros that exclude just the ASCII range
/regen/regcharclass.pl: white-space only; no code changes
regcharclass.h: Add macro for non-ASCII PATWS

This will be used to deprecate uses of non-ASCII Pattern White Space
regcomp.c: Add comments; no code changes
regcomp.c: Add macro for generating deprecated warnings

This will be used in a future commit
Add deprecation warning for literal PATWS under /x

This is explained in the perldelta changes in this commit.  We plan to
migrate to Unicode's definition of white-space to ignore under /x.  That
means we should raise a deprecation warning in the meantime if anyone
currently uses these characters in such a way as to have the meaning
changed when the migration is completed.
Typo in perl5178delta

Spotted by Hugo van der Sanden