Use test_path instead of which

which was used to detect icc, but on some platforms such as solaris 10
which always returns 0, even when the command is not found on the path.
This commit updates the invocation to use the test_path function
instead, which does return non-zero on solaris 10 in the failure case.

src/engine/build.sh

@@ -150,9 +150,9 @@ case $BOOST_JAM_TOOLSET in
     ;;
 
     intel-linux)
-    which icc >/dev/null 2>&1
+    test_path icc >/dev/null 2>&1
     if test $? ; then
-	BOOST_JAM_CC=`which icc`
+	BOOST_JAM_CC=`test_path icc`
 	echo "Found $BOOST_JAM_CC in environment"
 	BOOST_JAM_TOOLSET_ROOT=`echo $BOOST_JAM_CC | sed -e 's/bin.*\/icc//'`
 	# probably the most widespread