gcc6 build errors

[matthew-l-weber]

ar cru libargp.a argp-ba.o argp-eexst.o argp-fmtstream.o argp-help.o argp-parse.o argp-pv.o argp-pvh.o
/home/peko/autobuild/instance-0/output/host/bin/arc-buildroot-linux-uclibc-ranlib libargp.a
/home/peko/autobuild/instance-0/output/host/bin/arc-buildroot-linux-uclibc-gcc -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -matomic -Os -fPIC -ggdb3 -Wall -W -Wmissing-prototypes -Wmissing-declarations -Wstrict-prototypes -Waggregate-return -Wpointer-arith -Wbad-function-cast -Wnested-externs -o argp-test argp-test.o libargp.a
libargp.a(argp-help.o): In function indent_to': /home/peko/autobuild/instance-0/output/build/argp-standalone-1.3/argp-help.c:930: undefined reference to argp_fmtstream_point'
/home/peko/autobuild/instance-0/output/build/argp-standalone-1.3/argp-help.c:930: undefined reference to argp_fmtstream_point' /home/peko/autobuild/instance-0/output/build/argp-standalone-1.3/argp-help.c:932: undefined reference to argp_fmtstream_putc'
/home/peko/autobuild/instance-0/output/build/argp-standalone-1.3/argp-help.c:932: undefined reference to argp_fmtstream_putc' libargp.a(argp-help.o): In function space':
/home/peko/autobuild/instance-0/output/build/argp-standalone-1.3/argp-help.c:940: undefined reference to argp_fmtstream_point' /home/peko/autobuild/instance-0/output/build/argp-standalone-1.3/argp-help.c:940: undefined reference to argp_fmtstream_point'
/home/peko/autobuild/instance-0/output/build/argp-standalone-1.3/argp-help.c:944: undefined reference to argp_fmtstream_putc' /home/peko/autobuild/instance-0/output/build/argp-standalone-1.3/argp-help.c:944: undefined reference to argp_fmtstream_putc'
libargp.a(argp-help.o): In function `argp_doc':

Per a similar email thread, I believe the fix is adding -fgnu89-inline to the build env
https://www.mail-archive.com/ptxdist@pengutronix.de/msg09746.html