Include cstdlib for abs() with an int argument. Fixes the following
compile error with libc++.
source/exhumed/src/trigdat.cpp:159:9: error: call to 'abs' is ambiguous
if (abs(diff) > c)
^~~
/usr/include/c++/v1/math.h:761:1: note: candidate function
abs(float __lcpp_x) _NOEXCEPT {return ::fabsf(__lcpp_x);}
^
/usr/include/c++/v1/math.h:765:1: note: candidate function
abs(double __lcpp_x) _NOEXCEPT {return ::fabs(__lcpp_x);}
^
/usr/include/c++/v1/math.h:769:1: note: candidate function
abs(long double __lcpp_x) _NOEXCEPT {return ::fabsl(__lcpp_x);}
^
1 error generated.
