main: add missing locale.h include
This fixes the following build failure:
../src/main.c: In function ‘main’:
../src/main.c:217:3: warning: implicit declaration of function ‘setlocale’ [-Wimplicit-function-declaration]
217 | setlocale (LC_ALL, "");
| ^~~~~~~~~
../src/main.c:217:3: warning: nested extern declaration of ‘setlocale’ [-Wnested-externs]
../src/main.c:217:14: error: ‘LC_ALL’ undeclared (first use in this function)
217 | setlocale (LC_ALL, "");
| ^~~~~~
../src/main.c:217:14: note: each undeclared identifier is reported only once for each function it appears in
Edited by Jürg Billeter