[scripts] add patch-specs.sh, a utility for modifying GCC specs

[scripts] add patch-specs.sh, a utility for modifying GCC specs
The patch-specs.sh utility dumps the GCC specs of a given toolchain
and modifies them to always include $STAGING_DIR in the link and
compiler command lines, this makes most -I and -L flags unnecessary
and lets the compiler automatically find libraries and headers in
the staging dir, also solves the majority of -rpath issues.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@29767 3c298f89-4303-0410-b956-a3cf2f4a3e73