Fix C linkage build error in CSparse

[jlblancoc]

Changed apps/libraries

• mrpt-math

[codecov]

Codecov Report

Merging #1280 (c6be789) into develop (a57e0f3) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head c6be789 differs from pull request most recent head afda967. Consider uploading reports for the commit afda967 to get more accurate results

@@           Coverage Diff            @@
##           develop    #1280   +/-   ##
========================================
  Coverage    40.19%   40.19%           
========================================
  Files         1235     1235           
  Lines       106780   106781    +1     
========================================
+ Hits         42917    42918    +1     
  Misses       63863    63863           

Files Changed	Coverage Δ
libs/math/include/mrpt/math/CSparseMatrix.h	97.29% <ø> (ø)

... and 1 file with indirect coverage changes

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