bison yacc warning POSIX Yacc support %error-verbose [-Wyacc]

[robe]

Just noticed this on bessie32 when running. might be because I upgraded her as I don't recall seeing this before

bison -y -p wkt_yy -o'lwin_wkt_parse.c' -d lwin_wkt_parse.y
17:59:10 lwin_wkt_parse.y:114.1-14: warning: POSIX Yacc does not support %error-verbose [-Wyacc]

could also be that something triggered the rebuidling of this.

[pramsey]

Way below the threshold of concern

[Raúl Marín <git@…>]

In 60bb191/git:

Silence yacc warnings

References #4473
Closes ​https://github.com/postgis/postgis/pull/516/