CMake: allow generation of a Qt Compressed Help file for Clang source

r203272 enables generation of a Qt Compressed Help file for the LLVM source
code.

As a consequence, this change brings the same capabilities to Clang while
reusing these two variables:

  LLVM_ENABLE_DOXYGEN_QT_HELP
  LLVM_DOXYGEN_QHELPGENERATOR_PATH

and adding

  CLANG_DOXYGEN_QCH_FILENAME="org.llvm.clang.qch"
  CLANG_DOXYGEN_QHP_NAMESPACE="org.llvm.clang"
  CLANG_DOXYGEN_QHP_CUST_FILTER_NAME="Clang ${CLANG_VERSION}"
  CLANG_DOXYGEN_QHP_CUST_FILTER_ATTRS="Clang,${CLANG_VERSION}"

Patch by Konrad Kleine.

llvm-svn: 203801
diff --git a/clang/docs/doxygen.cfg.in b/clang/docs/doxygen.cfg.in
index 61c0bd8..2372e04 100644
--- a/clang/docs/doxygen.cfg.in
+++ b/clang/docs/doxygen.cfg.in
@@ -697,6 +697,59 @@
 
 TOC_EXPAND             = NO
 
+# If the GENERATE_QHP tag is set to YES and both QHP_NAMESPACE and 
+# QHP_VIRTUAL_FOLDER are set, an additional index file will be generated 
+# that can be used as input for Qt's qhelpgenerator to generate a 
+# Qt Compressed Help (.qch) of the generated HTML documentation.
+
+GENERATE_QHP           = @clang_doxygen_generate_qhp@
+
+# If the QHG_LOCATION tag is specified, the QCH_FILE tag can 
+# be used to specify the file name of the resulting .qch file. 
+# The path specified is relative to the HTML output folder.
+
+QCH_FILE               = @clang_doxygen_qch_filename@
+
+# The QHP_NAMESPACE tag specifies the namespace to use when generating 
+# Qt Help Project output. For more information please see 
+# http://qt-project.org/doc/qt-4.8/qthelpproject.html#namespace
+
+QHP_NAMESPACE          = @clang_doxygen_qhp_namespace@
+
+# The QHP_VIRTUAL_FOLDER tag specifies the namespace to use when generating 
+# Qt Help Project output. For more information please see 
+# http://qt-project.org/doc/qt-4.8/qthelpproject.html#virtual-folders
+
+QHP_VIRTUAL_FOLDER     = doc
+
+# If QHP_CUST_FILTER_NAME is set, it specifies the name of a custom filter to 
+# add. For more information please see 
+# http://qt-project.org/doc/qt-4.8/qthelpproject.html#custom-filters
+
+QHP_CUST_FILTER_NAME   = @clang_doxygen_qhp_cust_filter_name@
+
+# The QHP_CUST_FILT_ATTRS tag specifies the list of the attributes of the 
+# custom filter to add. For more information please see 
+# <a href="http://qt-project.org/doc/qt-4.8/qthelpproject.html#custom-filters"> 
+# Qt Help Project / Custom Filters</a>.
+
+QHP_CUST_FILTER_ATTRS  = @clang_doxygen_qhp_cust_filter_attrs@
+
+# The QHP_SECT_FILTER_ATTRS tag specifies the list of the attributes this 
+# project's 
+# filter section matches. 
+# <a href="http://qt-project.org/doc/qt-4.8/qthelpproject.html#filter-attributes"> 
+# Qt Help Project / Filter Attributes</a>.
+
+QHP_SECT_FILTER_ATTRS  = 
+
+# If the GENERATE_QHP tag is set to YES, the QHG_LOCATION tag can 
+# be used to specify the location of Qt's qhelpgenerator. 
+# If non-empty doxygen will try to run qhelpgenerator on the generated 
+# .qhp file.
+
+QHG_LOCATION           = @clang_doxygen_qhelpgenerator_path@
+
 # The DISABLE_INDEX tag can be used to turn on/off the condensed index at 
 # top of each HTML page. The value NO (the default) enables the index and 
 # the value YES disables it.