lang/hugs: unbreak with gcc5 or later

/tmp/ccbhQWJd.o: In function `hscore_get_errno':
PrelIOUtils.c:(.text+0x0): multiple definition of `hscore_get_errno'
/tmp/ccbhQWJd.o: In function `hscore_s_isreg':
PrelIOUtils.c:(.text+0x40): multiple definition of `hscore_s_isreg'
/tmp/ccH45HdH.o:Ptr.c:(.text+0x180): first defined here
/tmp/ccbhQWJd.o: In function `hscore_s_isdir':
PrelIOUtils.c:(.text+0x60): multiple definition of `hscore_s_isdir'
/tmp/ccH45HdH.o:Ptr.c:(.text+0x1a0): first defined here
/tmp/ccbhQWJd.o: In function `hscore_s_isfifo':
PrelIOUtils.c:(.text+0x80): multiple definition of `hscore_s_isfifo'
[...]

PR: 216707
Reported by: antoine (via exp-run)