Rename BR2_PREFER_STATIC_LIB to BR2_STATIC_LIBS

Since a while, the semantic of BR2_PREFER_STATIC_LIB has been changed
from "prefer static libraries when possible" to "use only static
libraries". The former semantic didn't make much sense, since the user
had absolutely no control/idea of which package would use static
libraries, and which packages would not. Therefore, for quite some
time, we have been starting to enforce that BR2_PREFER_STATIC_LIB
should really build everything with static libraries.

As a consequence, this patch renames BR2_PREFER_STATIC_LIB to
BR2_STATIC_LIBS, and adjust the Config.in option accordingly.

This also helps preparing the addition of other options to select
shared, shared+static or just static.

Note that we have verified that this commit can be reproduced by
simply doing a global rename of BR2_PREFER_STATIC_LIB to
BR2_STATIC_LIBS plus adding BR2_PREFER_STATIC_LIB to Config.in.legacy.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
diff --git a/Config.in.legacy b/Config.in.legacy
index b126556..09c025c 100644
--- a/Config.in.legacy
+++ b/Config.in.legacy
@@ -99,6 +99,18 @@
 endif
 
 ###############################################################################
+
+comment "Legacy options removed in 2015.02"
+
+config BR2_PREFER_STATIC_LIB
+	bool "static library option renamed"
+	select BR2_STATIC_LIBS
+	help
+	  The BR2_PREFER_STATIC_LIB was renamed to BR2_STATIC_LIBS. It
+	  highlights the fact that the option no longer "prefers"
+	  static libraries, but "enforces" static libraries (i.e
+	  shared libraries are completely unused).
+
 comment "Legacy options removed in 2014.11"
 
 config BR2_x86_generic