buildscript: Do not use target-dependent build directory

So far, building the firmware happens in parallel subdirectories
of "build", one for each subtarget. However, OpenWrt itself is
capable of hosting several target builds in its directory, so
there is no need for this extra separation.

This patch thus build all targets/subtargets directly in the
"build" folder.

Since most of the time during build is spent for the toolchain,
this will also significantly boost build time if more than one
target is used.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Fabian Bläse <fabian@blaese.de>

bsp/board_ar71xx.bsp

@@ -1,7 +1,6 @@
 machine=ar71xx
 chipset=ar71xx
 subtarget=tiny
-target=$builddir/$machine
 images=("openwrt-${chipset}-${subtarget}-archer-c25-v1-squashfs-sysupgrade.bin"
         "openwrt-${chipset}-${subtarget}-archer-c60-v1-squashfs-sysupgrade.bin"
         "openwrt-${chipset}-${subtarget}-archer-c7-v2-squashfs-sysupgrade.bin"

bsp/board_mt7621.bsp

@@ -1,7 +1,6 @@
 machine=mt7621
 chipset=ramips
 subtarget=mt7621
-target=$builddir/$machine
 
 images=(
         "openwrt-ramips-mt7621-ubnt-erx-squashfs-sysupgrade.tar"

bsp/board_wdr4900.bsp

@@ -1,7 +1,6 @@
 machine=wdr4900
 chipset=mpc85xx
 subtarget=generic
-target=$builddir/$machine
 
 images=(
         "openwrt-${chipset}-${subtarget}-tl-wdr4900-v1-squashfs-sysupgrade.bin"

buildscript

@@ -169,7 +169,7 @@ prepare() {
 
     #saves ~200MB for each build
     test -d ./src/dl || mkdir ./src/dl
-    ln -s ../../src/dl "$target"/dl
+    ln -s ../src/dl "$target"/dl
 }
 
 prebuild() {
@@ -347,6 +347,7 @@ loadBSP()
 {
     echo "Working with $(/bin/ls -l selected_bsp | awk '{ print $11 }')"
     . selected_bsp
+    target=$builddir
 }
 
 loadVariant()