m4: host-cpu-c-abi: add missing m4 from gnulib

The m4 file is a dependency of lib-prefix, leading to error at bootstrap because it was missing after update from commit 32b3f47b.

configure.ac:618: warning: gl_HOST_CPU_C_ABI_32BIT is m4_require'd but not m4_defun'd
m4/lib-prefix.m4:155: AC_LIB_PREPARE_MULTILIB is expanded from...
m4/lib-link.m4:181: AC_LIB_LINKFLAGS_BODY is expanded from...
m4/iconv.m4:10: AM_ICONV_LINKFLAGS_BODY is expanded from...
m4/gettext.m4:55: AM_GNU_GETTEXT is expanded from...
configure.ac:618: the top level
configure.ac:618: warning: gl_HOST_CPU_C_ABI_32BIT is m4_require'd but not m4_defun'd
m4/lib-prefix.m4:155: AC_LIB_PREPARE_MULTILIB is expanded from...
m4/lib-link.m4:181: AC_LIB_LINKFLAGS_BODY is expanded from...
m4/iconv.m4:10: AM_ICONV_LINKFLAGS_BODY is expanded from...
m4/gettext.m4:55: AM_GNU_GETTEXT is expanded from...
configure.ac:618: the top level
autoreconf: configure.ac: tracing
configure.ac:618: warning: gl_HOST_CPU_C_ABI_32BIT is m4_require'd but not m4_defun'd
m4/lib-prefix.m4:155: AC_LIB_PREPARE_MULTILIB is expanded from...
m4/lib-link.m4:181: AC_LIB_LINKFLAGS_BODY is expanded from...
m4/iconv.m4:10: AM_ICONV_LINKFLAGS_BODY is expanded from...
m4/gettext.m4:55: AM_GNU_GETTEXT is expanded from...
configure.ac:618: the top level