gcc-package-target.inc: add the symbol link /lib/cpp
When I was trying self-hosted-image, eglibc's do_install failed in the target:
ERROR: cannot stat bootparam_prot.h:
the cause is: rpcgen doesn't work properly: rpcgen can't exec /lib/cpp since
it doesn't exist.
According to http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/lib.html:
"if a C preprocessor is installed, /lib/cpp must be a reference to it, for
historical reasons. The usual placement of this binary is /usr/bin/cpp".
Typical distros, like Ubuntu, openSuSE, Fedora and RHEL, all comply with
the rule.
Actually in meta/recipes-devtools/gcc/gcc-package-target.inc, we do try to
package ${base_libdir}/cpp:
FILES_cpp = "\
${bindir}/${TARGET_PREFIX}cpp \
${base_libdir}/cpp \
${libexecdir}/gcc/${TARGET_SYS}/${BINV}/cc1"
But unluckily we didn't create a symbol link in do_install.
This patch adds the symbol link.
