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>

 commit 25bb77587944768581225d1c0048facab32cf019

 Author: Roberto Bagnara <bagnara@cs.unipr.it>

 Date:   Wed May 18 09:35:36 2011 +0200

     Moved misplaced conditional.

 diff --git a/interfaces/Java/tests/Makefile.am b/interfaces/Java/tests/Makefile.am

 index 64ba864..607bbc6 100644

 --- a/interfaces/Java/tests/Makefile.am

 +++ b/interfaces/Java/tests/Makefile.am

 @@ -51,6 +51,8 @@ Parma_Polyhedra_Library_test2.java \

  PPL_Test.java \

  ppl_java_tests_common

 +if ENABLE_SHARED

 +

  check_JAVA = \

  ppl_java_generated_tests.java \

  Test_Executor.java \

 @@ -62,8 +64,6 @@ Parma_Polyhedra_Library_test1.java \

  Parma_Polyhedra_Library_test2.java \

  PPL_Test.java

 -if ENABLE_SHARED

 -

  CLASSPATH = ../ppl_java.jar:.

  JAVACFLAGS = -classpath $(CLASSPATH)