Add generic_check function and add new default check target to build.sh.

The check target is excluded from the all target since it can often take a
very long time to run.

build.sh.generic

@@ -30,6 +30,12 @@ build()
     generic_build
 }
 
+reg check
+check()
+{
+    generic_check
+}
+
 reg install
 install()
 {