scripts/libc: do not build add-ons by default

Currently, no --enable-add-ons option is passed to libc configure when
"$(do_libc_add_ons_list ,)" is empty, which makes configure automatically search
for present add-ons. In that case, all present add-ons are built, although
no add-on was selected by the user in the config. Moreover, this can make the
configure fail if some non-standard add-ons like eglibc-localedef are present.

This behavior also leads to an inconsistency from a user point of view between
the following cases:
- LIBC_ADDONS_LIST="", LIBC_GLIBC_USE_PORTS=n and THREADS="none" in the config,
which makes "$(do_libc_add_ons_list ,)" return "", so all present add-ons
are built.
- LIBC_ADDONS_LIST="", LIBC_GLIBC_USE_PORTS=n and THREADS!="none" in the
config, which makes "$(do_libc_add_ons_list ,)" return the add-on supporting
the chosen threading implementation, e.g. "nptl", so only this add-on is
built.

This patch disables the building of all add-ons in that case.

It is still possible to build all present add-ons by adding --enable-add-ons to
LIBC_GLIBC_EXTRA_CONFIG_ARRAY.

Signed-off-by: "Benoît THÉBAUDEAU" <benoit.thebaudeau@advansee.com>

 The m68k mcpu processor does not like unaligned access

 Disable at least mcpu32, m68010 and m68020. These processors certainly

 do not like unaligned accesses.

 Signed-off-by: Remy Bohmer <linux@bohmer.net>

 [yann.morin.1998@anciens.enib.fr: update for 1.19.0 from 1.18.0]

 Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 ---

  newlib/libc/machine/m68k/memcpy.S |    2 +-

  1 file changed, 1 insertion(+), 1 deletion(-)

 Index: newlib-1.19.0/newlib/libc/machine/m68k/memcpy.S

 ===================================================================

 --- newlib-1.19.0.orig/newlib/libc/machine/m68k/memcpy.S

 +++ newlib-1.19.0/newlib/libc/machine/m68k/memcpy.S

 @@ -15,7 +15,7 @@

  #include "m68kasm.h"

 -#if defined (__mcoldfire__) || defined (__mc68010__) || defined (__mc68020__) || defined (__mc68030__) || defined (__mc68040__) || defined (__mc68060__)

 +#if defined (__mcoldfire__) || defined (__mc68030__) || defined (__mc68040__) || defined (__mc68060__)

  # define MISALIGNED_OK 1

  #else

  # define MISALIGNED_OK 0