Safe version of ascii macros, add missing tolower_ascii

[vnlitvinov]

• fixes a warning introduced in PERF: ascii c string functions #23981
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

Using unparenthesized macro parameters is dangerous, so wrap c in braces.

Example warning fixed by adding tolower_ascii():

In file included from pandas/_libs/lib.c:643:0:
pandas/_libs/src/parse_helper.h: In function ‘lowercase’:
pandas/_libs/src/parse_helper.h:141:26: warning: implicit declaration of function ‘tolower_ascii’; did you mean ‘toupper_ascii’? [-Wimplicit-function-declaration]
     for (; *p; ++p) *p = tolower_ascii(*p);
                          ^~~~~~~~~~~~~
                          toupper_ascii

[chris-b1]

lgtm - thanks! I did this originally, I always forget the right wrapping to make macros safe(er)
@jreback

[codecov]

Codecov Report

Merging #25836 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #25836      +/-   ##
==========================================
- Coverage    91.3%    91.3%   -0.01%     
==========================================
  Files         173      173              
  Lines       53004    53004              
==========================================
- Hits        48397    48396       -1     
- Misses       4607     4608       +1

Flag	Coverage Δ
#multiple	89.87% <ø> (ø)	⬆️
#single	41.77% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/util/testing.py	89.3% <0%> (-0.11%)	⬇️

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[jreback]

thanks @vnlitvin