MFH: r551664

finance/beancount: fix build on GCC architectures

Use C11 compiler:
beancount/parser/lexer.c:172: error: redefinition of typedef 'yyscan_t'
beancount/parser/parser.h:11: error: previous declaration of 'yyscan_t' was here

Approved by: portmgr (fix build blanket)