Bump PORTREVISION for ports depending on the canonical version of GCC

defined via Mk/bsd.default-versions.mk which has moved from GCC 7.4 t
GCC 8.2 under most circumstances.

This includes ports
 - with USE_GCC=yes or USE_GCC=any,
 - with USES=fortran,
 - using Mk/bsd.octave.mk which in turn features USES=fortran, and
 - with USES=compiler specifying openmp, nestedfct, c11, c++0x, c++11-lang,
   c++11-lib, c++14-lang, c++17-lang, or gcc-c++11-lib
plus, as a double check, everything INDEX-11 showed depending on lang/gcc7.

PR:		231590

math/py-gnuplot/Makefile

@@ -3,7 +3,7 @@
 
 PORTNAME=	gnuplot
 PORTVERSION=	1.8
-PORTREVISION=	8
+PORTREVISION=	9
 CATEGORIES=	math python
 MASTER_SITES=	SF/${PORTNAME}-py/Gnuplot-py/${PORTVERSION}
 PKGNAMEPREFIX=	${PYTHON_PKGNAMEPREFIX}