[cmake] Remove deprecated GetSVN.cmake parameters

[modocache]

Summary

Depends on https://reviews.llvm.org/D35133.

As of https://reviews.llvm.org/D35133, Clang will have migrated to the
new parameter lists in GetSVN.cmake: SOURCE_DIRS and NAMES. Remove
the old parameters, FIRST_SOURCE_DIR/FIRST_NAME and
SECOND_SOURCE_DIR/SECOND_NAME.

Other external projects using LLVM's GetSVN.cmake, such as Apple's
Swift, will also be forced to migrate.

Test Plan:

1. Perform a clean build of Clang, verify that clang --version still prints the correct LLVM and Clang revision information.
2. Apply this patch, then perform another clean build. clang --version should still print the correct revision information.

[jordan_rose]

Rather than delete these outright, it's probably polite to error on the presence of FIRST_SOURCE_DIR. There might be other out-of-tree projects that need to update.

[modocache]

Good idea, thanks! I'll do so.

cmake/modules/GetSVN.cmake

if (DEFINED SOURCE_DIRS AND DEFINED NAMES)
   math(EXPR source_dirs_max_index ${source_dirs_length}-1)
   foreach(index RANGE ${source_dirs_max_index})
     list(GET SOURCE_DIRS ${index} source_dir)
     list(GET NAMES ${index} name)
     append_info(${name} ${source_dir})
   endforeach()
 endif()
 
-# Allow -DFIRST_SOURCE_DIR arguments until Clang migrates to the new
-# -DSOURCE_DIRS argument.
-if(DEFINED FIRST_SOURCE_DIR)
-  append_info(${FIRST_NAME} "${FIRST_SOURCE_DIR}")
-  if(DEFINED SECOND_SOURCE_DIR)
-    append_info(${SECOND_NAME} "${SECOND_SOURCE_DIR}")
-  endif()
-endif()
-
 # Copy the file only if it has changed.
 execute_process(COMMAND ${CMAKE_COMMAND} -E copy_if_different
   "${HEADER_FILE}.txt" "${HEADER_FILE}")
 file(REMOVE "${HEADER_FILE}.txt")