gcc: target: fix libiberty removal

- use ${libdir} instead of ${exec_prefix}/lib

Fix the following warning:
WARNING: QA Issue: gcc: Files/directories were installed but not shipped
  /usr/lib64/libiberty.a

(From OE-Core rev: b3643415ad91dc77880cc5b95e9ad8cd9aef5c44)

Signed-off-by: Constantin Musca <constantinx.musca@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/gcc/gcc-4.7.inc

@@ -1,6 +1,6 @@
 require gcc-common.inc
 
-PR = "r15"
+PR = "r16"
 
 # Third digit in PV should be incremented after a minor release
 # happens from this branch on gcc e.g. currently its 4.7.1

meta/recipes-devtools/gcc/gcc-package-target.inc

@@ -115,8 +115,8 @@ do_install () {
 	rm -f *gcc-?.?*
 
 	# We use libiberty from binutils
-	find ${D}${exec_prefix}/lib -name libiberty.a | xargs rm -f
-	find ${D}${exec_prefix}/lib -name libiberty.h | xargs rm -f
+	find ${D}${libdir} -name libiberty.a | xargs rm -f
+	find ${D}${libdir} -name libiberty.h | xargs rm -f
 
 	# Not sure why we end up with these but we don't want them...
 	rm -f ${TARGET_PREFIX}${TARGET_PREFIX}*