android-rebuild.sh: Better parallel builds.

This patch computes the number of CPUs on the host to
automatically used it with 'make -j<number>'.

Change-Id: If4e2d8b159662f5b7f02e8e48447b9916e7051b2

android-rebuild.sh

@@ -6,8 +6,22 @@
 # assume that the device tree is in TOP
 #
 
+case $(uname -s) in
+    Linux)
+        HOST_NUM_CPUS=`cat /proc/cpuinfo | grep processor | wc -l`
+        ;;
+    Darwin|FreeBsd)
+        HOST_NUM_CPUS=`sysctl -n hw.ncpu`
+        ;;
+    CYGWIN*|*_NT-*)
+        HOST_NUM_CPUS=$NUMBER_OF_PROCESSORS
+        ;;
+    *)  # let's play safe here
+        HOST_NUM_CPUS=1
+esac
+
 cd `dirname $0`
-./android-configure.sh $* && \
-make clean && \
-make -j4 && \
+rm -rf objs &&
+./android-configure.sh $@ &&
+make -j$HOST_NUM_CPUS &&
 echo "Done. !!"