gcc-package-target: add libexec for plugin

Fixes:

ERROR: For recipe gcc, the following files/directories were installed but not shipped in any package:
ERROR:   /usr/libexec/gcc/i586-poky-linux/4.7.1/plugin/gengtype
(From OE-Core rev: 0be64cda0a20ca3aab75ee0cc360236d2dc40c95)

Signed-off-by: Saul Wold <sgw@linux.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 = "r0"
+PR = "r1"
 
 # Third digit in PV should be incremented after a minor release
 # happens from this branch on gcc e.g. currently its 4.7.0

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

@@ -36,7 +36,7 @@ FILES_${PN}-dev = "\
 "
 FILES_${PN}-plugin-dev = "\
   ${gcclibdir}/${TARGET_SYS}/${BINV}/plugin/include/ \
-  ${gcclibdir}/${TARGET_SYS}/${BINV}/plugin/gengtype \
+  ${libexecdir}/gcc/${TARGET_SYS}/${BINV}/plugin/gengtype \
   ${gcclibdir}/${TARGET_SYS}/${BINV}/plugin/gtype.state \
 "
 FILES_${PN}-symlinks = "\