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>

 diff -p -c -u -r1.196 elf32-arm.c

 diff -durN binutils-2.20.1.orig/bfd/elf32-arm.c binutils-2.20.1/bfd/elf32-arm.c

 --- binutils-2.20.1.orig/bfd/elf32-arm.c	2010-02-22 09:06:48.000000000 +0100

 +++ binutils-2.20.1/bfd/elf32-arm.c	2010-08-17 19:32:25.000000000 +0200

 @@ -3194,11 +3194,15 @@

  	  /* We have an extra 2-bytes reach because of

  	     the mode change (bit 24 (H) of BLX encoding).  */

 +	  /* A stub is needed only if this call is not throught a PLT

 +	     entry, because PLT stubs handle mode switching

 +	     already.  */

  	  if (branch_offset > (ARM_MAX_FWD_BRANCH_OFFSET + 2)

  	      || (branch_offset < ARM_MAX_BWD_BRANCH_OFFSET)

 -	      || ((r_type == R_ARM_CALL) && !globals->use_blx)

 -	      || (r_type == R_ARM_JUMP24)

 -	      || (r_type == R_ARM_PLT32))

 +	      || ( (((r_type == R_ARM_CALL) && !globals->use_blx)

 +		    || (r_type == R_ARM_JUMP24)

 +		    || (r_type == R_ARM_PLT32))

 +		   && !use_plt))

  	    {

  	      stub_type = (info->shared | globals->pic_veneer)

  		/* PIC stubs.  */