error: use of undeclared identifier 'errno'
pango 1.50.1 fails to build for me on macOS 10.15.7. Grepping my build log for "error:" I see:
../pango-1.50.1/pango/json/gtkjsonparser.c:1475:3: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1478:7: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1480:11: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1480:20: error: use of undeclared identifier 'ERANGE'
../pango-1.50.1/pango/json/gtkjsonparser.c:1483:62: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1509:3: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1517:7: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1519:11: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1519:20: error: use of undeclared identifier 'ERANGE'
../pango-1.50.1/pango/json/gtkjsonparser.c:1522:62: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1553:3: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1561:7: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1563:11: error: use of undeclared identifier 'errno'
../pango-1.50.1/pango/json/gtkjsonparser.c:1563:20: error: use of undeclared identifier 'ERANGE'
../pango-1.50.1/pango/json/gtkjsonparser.c:1566:62: error: use of undeclared identifier 'errno'
Adding #include <errno.h>
to that file fixes it.