New CMake module to locate libconfig++

The current code to locate libconfig++ has some trouble:
- It is located in the main CMakeList file but should be a module of its own
- It depends on pkg-config which is not available on Windows
- The returned values are not really useful therefore the library name is hard coded

This commit tries to solve these problems. For a Unix-like system there should be no difference.
Additionally, you can override the variables on the command line which is useful for builds on Windows.

CMakeLists.txt

@@ -23,25 +23,7 @@ find_package(LLVM 3.0 EXACT REQUIRED
 #
 # Locate libconfig++.
 #
-
-include(FindPkgConfig)
-if(PKG_CONFIG_FOUND)
-    pkg_search_module(LIBCONFIGPP libconfig++)
-    if(LIBCONFIGPP_FOUND)
-        set(LIBCONFIG_CXXFLAGS ${LIBCONFIGPP_CFLAGS} CACHE STRING "libconfig++ compiler flags")
-        set(LIBCONFIG_LDFLAGS ${LIBCONFIGPP_LDFLAGS} CACHE STRING "libconfig++ linker flags")
-    endif()
-else()
-    message(WARNING "pkg-config not found. libconfig++ options cannot be detected, you might need to set them manually.")
-endif()
-
-# libconfig++ is actually a required dependency, but has never been defined as
-# one – maybe there was a problem with the auto detection once.
-if (NOT LIBCONFIGPP_FOUND)
-    set(LIBCONFIG_CXXFLAGS "" CACHE STRING "libconfig++ compiler flags")
-    set(LIBCONFIG_LDFLAGS "" CACHE STRING "libconfig++ linker flags")
-    message(WARNING "libconfig++ not found. If compilation fails but the library is installed, consider manually setting the LIBCONFIG_CXXFLAGS and LIBCONFIG_LDFLAGS CMake variables.")
-endif()
+find_package(LibConfig++ REQUIRED)
 
 #
 # Main configuration.
@@ -277,6 +259,7 @@ include_directories(
     ${PROJECT_BINARY_DIR}/${DMDFE_PATH}
     ${PROJECT_SOURCE_DIR}
     ${LLVM_INCLUDE_DIRS}
+    ${LIBCONFIG++_INCLUDE_DIR}
 )
 
 if(MSVC)
@@ -353,7 +336,7 @@ set_target_properties(
     RUNTIME_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/bin
     COMPILE_FLAGS "${LLVM_CXXFLAGS} ${LIBCONFIG_CXXFLAGS} ${EXTRA_CXXFLAGS}"
 )
-target_link_libraries(${LDC_EXE} ${LDC_LIB} ${LIBCONFIG_LDFLAGS} config++)
+target_link_libraries(${LDC_EXE} ${LDC_LIB} ${LIBCONFIG_LDFLAGS} ${LIBCONFIG++_LIBRARY})
 
 # For use by the druntime/Phobos build system.
 get_target_property(LDC_LOC ${LDC_EXE} LOCATION)

cmake/Modules/FindLibConfig++.cmake

@@ -0,0 +1,24 @@
+# Find the libconfig++ includes and library
+#
+# This module defines
+# LIBCONFIG++_INCLUDE_DIR, where to find libconfig++ include files, etc.
+# LIBCONFIG++_LIBRARy, the library to link against to use libconfig++.
+# LIBCONFIG++_FOUND, If false, do not try to use libconfig++.
+
+# also defined, but not for general use are
+# LIBCONFIG++_LIBRARY, where to find the libconfig++ library.
+
+set(LIBCONFIG++_FOUND TRUE)
+
+find_path(LIBCONFIG++_INCLUDE_DIR libconfig.h++)
+
+find_library(LIBCONFIG++_LIBRARY config++)
+
+if (LIBCONFIG++_INCLUDE_DIR AND LIBCONFIG++_LIBRARY)
+   set(LIBCONFIG++_FOUND TRUE)
+endif (LIBCONFIG++_INCLUDE_DIR AND LIBCONFIG++_LIBRARY)
+
+# Use the default CMake facilities for handling QUIET/REQUIRED.
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(LLVM
+    REQUIRED_VARS LIBCONFIG++_INCLUDE_DIR LIBCONFIG++_LIBRARY)