fbcode_builder: ThriftCppLibrary: the output depends on the thrift templates

Summary:
Update ThriftCppLibrary.cmake to record that the output depends on the thrift
`cpp2` template files.  The `THRIFT_TEMPLATE_FILES` variable was defined in
D16062657 but doesn't appear to be used anywhere.  This uses it, and also
updates it to only match the C++ template files.

Reviewed By: wez

Differential Revision: D16738442

fbshipit-source-id: aa4097e9ec1d009ef1e3ee2efd03ffa19a82ed12

build/fbcode_builder/CMake/ThriftCppLibrary.cmake

@@ -77,7 +77,7 @@ function(add_thrift_cpp2_library LIB_NAME THRIFT_FILE)
 
   file(
     GLOB_RECURSE THRIFT_TEMPLATE_FILES
-    FOLLOW_SYMLINKS "${FBTHRIFT_TEMPLATES_DIR}/*.mustache"
+    FOLLOW_SYMLINKS "${FBTHRIFT_TEMPLATES_DIR}/cpp2/*.mustache"
   )
 
   # Emit the rule to run the thrift compiler
@@ -101,6 +101,7 @@ function(add_thrift_cpp2_library LIB_NAME THRIFT_FILE)
       "${THRIFT_FILE}"
     DEPENDS
       ${ARG_DEPENDS}
+      ${THRIFT_TEMPLATE_FILES}
   )
 
   # Now emit the library rule to compile the sources