Apply suggestions from code review

Co-authored-by: Johel Ernesto Guerrero Peña <[email protected]>

Author: jensmaurer

source/lib-intro.tex

@@ -157,7 +157,7 @@
 Equivalently, a call to a C standard library function is
 a non-constant library call
 if \tcode{errno} is set
-when math \tcode{errhandling \& MATH ERRNO} is \tcode{true}.
+when \tcode{math_errhandling \& MATH_ERRNO} is \tcode{true}.
 \end{note}
 
 \rSec1[description]{Method of description}