xbps-src: added XBPS_LDFLAGS into the configuration file.

This is to specify common LDFLAGS settings for all packages, by default
it's set to '-Wl,--as-needed' to avoid linking extra libraries into
the binaries. This helped to find such cases.

xbps-src/etc/xbps-src.conf

@@ -19,6 +19,15 @@ XBPS_MASTERDIR=$XBPS_DISTRIBUTIONDIR/masterdir
 XBPS_CFLAGS="-O2 -pipe"
 XBPS_CXXFLAGS="$XBPS_CFLAGS"
 
+#
+# Linker flags passed to the compiler. By default we use --as-needed to
+# avoid linking extra libraries into binaries. See the following link
+# for info:
+#
+# http://www.gentoo.org/proj/en/qa/asneeded.xml
+#
+XBPS_LDFLAGS="-Wl,--as-needed"
+
 #
 # Number of jobs when running make(1)-alike commands.
 #