Use hw.ncpu sysctl on FreeBSD to determine processor count.

Patch by Mike Meyer.

http://code.google.com/p/phantomjs/issues/detail?id=597

build.sh

@@ -19,17 +19,20 @@ elif [[ $OSTYPE = darwin* ]]; then
    # We only support modern Mac machines, they are at least using
    # hyperthreaded dual-core CPU.
    COMPILE_JOBS=4
+elif [[ $OSTYPE == freebsd* ]]; then
+   COMPILE_JOBS=`sysctl -n hw.ncpu`
 else
    CPU_CORES=`grep -c ^processor /proc/cpuinfo`
    if [[ "$CPU_CORES" -gt 1 ]]; then
        COMPILE_JOBS=$CPU_CORES
-       if [[ "$COMPILE_JOBS" -gt 8 ]]; then
-           # Safety net.
-           COMPILE_JOBS=8
-       fi
    fi
 fi
 
+if [[ "$COMPILE_JOBS" -gt 8 ]]; then
+   # Safety net.
+   COMPILE_JOBS=8
+fi
+
 until [ -z "$1" ]; do
     case $1 in
         "--qt-config")