redeclaration of 'yyleng' with a different type: 'int' vs 'yy_size_t'

[ibrokemypie]

Fails to build on macOS with following error:

[ 87%] Building C object CMakeFiles/pkgparse.dir/pkgbuild_scanner.c.o
pkgbuild_scanner.l:30:13: error: redeclaration of 'yyleng' with a different type: 'int' vs 'yy_size_t' (aka 'unsigned long')
        extern int yyleng;
                   ^
/Users/conor/git/pkgparse/pkgbuild_scanner.c:276:11: note: previous definition is here
yy_size_t yyleng;
          ^
1 error generated.