add default arguments for xcodebuild and scan-build

to make plugin usable out of box

Author: 临寒

src/main/resources/jenkins/plugins/clangscanbuild/ClangScanBuildBuilder/config.jelly

@@ -35,11 +35,11 @@
   		</f:entry>
 
   		<f:entry title="Additional scan-build arguments" field="scanbuildargs">
-    		<f:textbox default="" />
+    		<f:textbox default="--use-analyzer Xcode" />
   		</f:entry>
 
                 <f:entry title="Additional xcode build arguments" field="xcodebuildargs">
-    		<f:textbox default="" />
+    		<f:textbox default="-derivedDataPath $WORKSPACE/build" />
   		</f:entry>
 
 	</f:advanced>

src/main/resources/jenkins/plugins/clangscanbuild/ClangScanBuildBuilder/help-scanbuildargs.html

@@ -1,2 +1,8 @@
 This field can be used to pass additional arguments to clang scan-build.  The arguments will appear before the xcodebuild sub command.  
-You can view the assembled command by viewing the job's build console.
+You can view the assembled command by viewing the job's build console.
+<br/><br/>
+scan-build uses the 'clang' executable relative to itself for static analysis by default.
+<br/>
+<i><b>--use-analyzer Xcode</b></i> using the 'clang' packaged with Xcode (on OS X)
+<br/>
+<i><b>--use-analyzer [path to clang]</b></i> to use the 'clang' from <i>'path to clang'</i> or <i>$PATH</i> if no path specified.

src/main/resources/jenkins/plugins/clangscanbuild/ClangScanBuildBuilder/help-xcodebuildargs.html

@@ -1,2 +1,4 @@
 This field can be used to pass additional arguments to clang scan-build.  The arguments will appear after the xcodebuild sub command.
-You can view the assembled command by viewing the job's build console.
+You can view the assembled command by viewing the job's build console.
+<br/><br/>
+<i><b>-derivedDataPath $WORKSPACE/build</b></i> is to save build products and other derived data to <i>build</i> directory under current workspace