Log Message:
link-grammar: update to 5.8.1

Version 5.8.1 (8 January 2021)
 * Fix macOS/SunOS build break.
 * English dict: fix numerical identifiers used as adjectives.
 * English dict: fix post-posed Latin adjectival modifiers.
 * Merge upstream gentoo patches. #1102
 * Make -O3 default for CFLAGS/CXXFLAGS, but overridable by the user.
 * English dict: fix look_at, listen_to person-action
 * English dict: fix verb "felt" with object-action.
 * English dict: fix why-perform-action questions.
 * Fix race condition in spell-guesser. #1122 #1123