Add -fbuiltin-headers-in-system-modules to clang-scan-deps test

One of the things this test is checking for is that builtin headers get
the correct path in Darwin system modules. Add
-fbuiltin-headers-in-system-modules explicitly so that the test does not
depend on the SDK version.

rdar://133239616
(cherry picked from commit 55d362b)

Author: benlangmuir

clang/test/ClangScanDeps/modules-include-tree-prefix-map.c

@@ -315,7 +315,7 @@
 [{
   "file": "DIR/tu.m",
   "directory": "DIR",
-  "command": "CLANG -target x86_64-apple-darwin10 -fsyntax-only DIR/tu.m -I DIR -isystem DIR/System -fmodules -fimplicit-modules -fimplicit-module-maps -fmodules-cache-path=DIR/module-cache -Rcompile-job-cache"
+  "command": "CLANG -target x86_64-apple-darwin10 -fsyntax-only DIR/tu.m -I DIR -isystem DIR/System -fmodules -fimplicit-modules -fimplicit-module-maps -fmodules-cache-path=DIR/module-cache -Rcompile-job-cache -Xclang -fbuiltin-headers-in-system-modules"
 }]
 
 //--- module.modulemap