build: override hardcoded paths to bison and m4 to make the SDK more relocatable

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42300 3c298f89-4303-0410-b956-a3cf2f4a3e73
target/toolchain: strip files, leave out the initial gcc

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42302 3c298f89-4303-0410-b956-a3cf2f4a3e73