It’s not worth the porting hassle, and as the glibc manual says,
“this function is generally a poor choice for processing strings”.
* admin/merge-gnulib (GNULIB_MODULES): Remove stpncpy.
* exec/configure.ac: Do not check for stpncpy.
* exec/exec.c (rpl_stpncpy, stpncpy): Remove this replacement.
(exec_0): Properly clear buffer1.  Use memcpy instead of
stpncpy to add the trailing name.  This code is clearly
still suboptimal but efficiency is not that important here
and I tried to minimize the change.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.

* admin/merge-gnulib (GNULIB_MODULES):
* cross/lib/getopt-pfx-core.h (optind):
* cross/lib/limits.in.h (BOOL_WIDTH):
* cross/lib/math.in.h:
* cross/lib/stpncpy.c (__stpncpy):
* cross/lib/string.in.h:
* lib/getopt-pfx-core.h (optind):
* lib/gnulib.mk.in (ANDROID_MIN_SDK):
(GL_COND_OBJ_STDIO_READ_CONDITION):
(LIBS):
(NDK_BUILD_AR):
(REPLACE__EXIT):
(libgnu_a_SOURCES):
* lib/limits.in.h (BOOL_WIDTH):
* lib/math.in.h:
* lib/stpncpy.c (__stpncpy):
* lib/string.in.h:
* m4/assert_h.m4 (gl_ASSERT_H):
* m4/fdopendir.m4 (gl_FUNC_FDOPENDIR):
* m4/getdelim.m4 (gl_FUNC_GETDELIM):
* m4/getline.m4 (gl_FUNC_GETLINE):
* m4/gnulib-common.m4 (gl_COMMON_BODY):
(gl_CONDITIONAL_HEADER):
(gl_CHECK_FUNCS_ANDROID):
* m4/gnulib-comp.m4 (gl_EARLY):
(gl_INIT):
(gl_FILE_LIST):
* m4/limits-h.m4:
* m4/lstat.m4 (gl_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK):
* m4/malloc.m4 (_AC_FUNC_MALLOC_IF):
* m4/printf.m4 (gl_PRINTF_SIZES_C99):
(gl_PRINTF_INFINITE):
(gl_PRINTF_INFINITE_LONG_DOUBLE):
(gl_PRINTF_DIRECTIVE_A):
(gl_PRINTF_DIRECTIVE_F):
(gl_PRINTF_FLAG_ZERO):
(gl_SNPRINTF_PRESENCE):
(gl_SNPRINTF_DIRECTIVE_N):
(gl_VSNPRINTF_ZEROSIZE_C99):
* m4/pselect.m4 (gl_FUNC_PSELECT):
* m4/readlink.m4 (gl_FUNC_READLINK):
* m4/realloc.m4 (_AC_FUNC_REALLOC_IF):
* m4/signbit.m4 (gl_SIGNBIT):
* m4/stpncpy.m4 (gl_FUNC_STPNCPY):
* m4/symlink.m4 (gl_FUNC_SYMLINK): Add gnulib module stpncpy.
* src/android.c: Include string.h.