multilib: Add support for compiling recipes against multiple ABIs

This patch adds the core multilib class which can be used along with a
parameter specifying the mutlilib to use in BBCLASSEXTEND.

The MLPREFIX variable is added and can be used in cases where its too
difficult to dynmaically work out where a mutltilib prefix is needed
to be added to a variable.

This includes:
  * SHLIBSDIR and PACKAGE_ARCH fixes from Lianhao Lu.
  * PACKAGE_DYNAMIC mapping from Yu Ke
  * PACKAGE_INSTALL mapping from Yu Ke
  * RPROVIDES mapping from Yu Ke
  * TARGET_VENDOR fix from Mark Hatle
  * Ignorning *-native-runtime dependnecies as well as *-native from Yu Ke
  * Map PKG and ALLOW_EMPTY from Dongxiao Xu
  * Ensure RCONFLICTS and PKG field dependencies are remapped (from Dongxiao Xu)
  * Ensure PN and MLPREFIX are set at the same time to ensure consistent BPN values (Yu Ke)

(From OE-Core rev: 5d9453049915db48ec4b5972e12287417ebb61a2)

Signed-off-by: Yu Ke <ke.yu@intel.com>
Signed-off-by: Xu Dongxiao <dongxiao.xu@intel.com>
Signed-off-by: Lianhao Lu <lianhao.lu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/package.bbclass

@@ -168,6 +168,17 @@ python () {
         bb.data.setVarFlag('do_package', 'deptask', " ".join(deps), d)
     else:
         d.setVar("PACKAGERDEPTASK", "")
+
+    multilib_archs = []
+    multilibs= d.getVar('MULTILIBS', True) or ""
+    if multilibs:
+        for ext in multilibs.split():
+            eext = ext.split(':')
+            if len(eext) > 1:
+                if eext[0] == 'multilib':
+                    multilib_archs.append('ml' + eext[1])
+
+    d.setVar("MULTILIB_ARCHS", ' '.join(multilib_archs))
 }
 
 def splitfile(file, debugfile, debugsrcdir, d):