Add "-std=c99" to cflags implicitly

[methane]

Fixes #460.

[codecov]

Codecov Report

Merging #468 (9e96c2f) into master (401ca82) will decrease coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #468      +/-   ##
==========================================
- Coverage   86.66%   86.60%   -0.07%     
==========================================
  Files          12       12              
  Lines        1530     1530              
==========================================
- Hits         1326     1325       -1     
- Misses        204      205       +1     

Impacted Files	Coverage Δ
MySQLdb/cursors.py	80.80% <0.00%> (-0.41%)	⬇️

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[lgtm-com]

This pull request fixes 1 alert when merging 9e96c2f into 401ca82 - view on LGTM.com

fixed alerts:

• 1 for Module is imported with 'import' and 'import from'