science/svmlight: fix build on 13.0+

cc -O2 -pipe  -fPIC -fstack-protector-strong -fno-strict-aliasing  svm_learn_main.o svm_learn.o svm_common.o svm_hideo.o -o svm_learn -L. -lm
ld: error: duplicate symbol: verbosity
>>> defined at svm_common.c
>>>            svm_common.o:(verbosity)
>>> defined at svm_hideo.c
>>>            svm_hideo.o:(.bss+0x38)
cc: error: linker command failed with exit code 1 (use -v to see invocation)

science/svmlight/Makefile

@@ -19,7 +19,7 @@ LICENSE_PERMS=	# none
 MAINTAINER=	ports@FreeBSD.org
 COMMENT=	Implementation of Support Vector Machines (SVMs) in C
 
-CFLAGS+=	-fPIC
+CFLAGS+=	-fPIC -fcommon
 MAKE_ARGS=	CC="${CC}" CFLAGS="${CFLAGS}" LD="${CC}" LFLAGS="${CFLAGS}"
 NO_WRKSUBDIR=	yes
 USES=		gmake