Mac OS does not correctly support the math library long double constants

[simoninns]

This causes and issue compiling the ld-decode-tools ld-comb-ntsc on mac:

comb.cpp:732:83: error: use of undeclared identifier 'M_PIl'; did you mean
'P_PID'?
...double>(y), x) * (180 / M_PIl));
^~~~~
P_PID

This can be fixed by defining the constant by hand:

#ifndef M_PIl
#define M_PIl 0xc.90fdaa22168c235p-2L
#endif

[simoninns]

Closing as fixed (no Mac environment to test on) - reopen if the problem is still there.