Using GCC 9 one can see:

$ /bin/sh ../libtool  --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I. -I.. 
-I.. -I../autoopts  -DPKGDATADIR='"/usr/local/share/autogen"' -g -O2
-Wno-format-contains-nul -fno-strict-aliasing -Wall -Werror -Wcast-align
-Wmissing-prototypes -Wpointer-arith -Wshadow -Wstrict-prototypes
-Wwrite-strings -Wstrict-aliasing=3 -Wextra -Wno-cast-qual -g -O2
-Wno-format-contains-nul -fno-strict-aliasing -c -o libopts_la-libopts.lo `test
-f 'libopts.c' || echo './'`libopts.c
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I.. -I.. -I../autoopts
-DPKGDATADIR=\"/usr/local/share/autogen\" -g -O2 -Wno-format-contains-nul
-fno-strict-aliasing -Wall -Werror -Wcast-align -Wmissing-prototypes
-Wpointer-arith -Wshadow -Wstrict-prototypes -Wwrite-strings
-Wstrict-aliasing=3 -Wextra -Wno-cast-qual -g -O2 -Wno-format-contains-nul
-fno-strict-aliasing -c libopts.c  -fPIC -DPIC -o .libs/libopts_la-libopts.o
In file included from autoopts.c:42,
                 from libopts.c:22:
In function ���canonicalize_pathname���,
    inlined from ���option_pathfind.constprop��� at ../compat/pathfind.c:88:32:
../compat/pathfind.c:214:17: error: ���strcpy��� accessing 1 byte at offsets [0,
9223372036854775807] and [0, 9223372036854775807] may overlap 1 byte at offset
0 [-Werror=restrict]
  214 |                 strcpy( result + start + 1, result + i + 2 );
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

It's analyzed here:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88973

and it looks it's a real issue.