FindRuby: clean up querying variables from Ruby

Newer Ruby versions (from 1.9 onward) seem to warn if you query Config::CONFIG
and print a warning to use RbConfig instead. RbConfig seems to also work in
older versions, at least in 1.8. Use a macro to query RbConfig first and only
if that doesn't give anything fall back to Config.

Modules/FindRuby.cmake

@@ -61,49 +61,44 @@ FIND_PROGRAM(RUBY_EXECUTABLE NAMES ${_RUBY_POSSIBLE_EXECUTABLE_NAMES})
 
 
 IF(RUBY_EXECUTABLE  AND NOT  RUBY_VERSION_MAJOR)
-  # query the ruby version
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['MAJOR']"
-      OUTPUT_VARIABLE RUBY_VERSION_MAJOR)
+  FUNCTION(_RUBY_CONFIG_VAR RBVAR OUTVAR)
+    EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print RbConfig::CONFIG['${RBVAR}']"
+      RESULT_VARIABLE _RUBY_SUCCESS
+      OUTPUT_VARIABLE _RUBY_OUTPUT
+      ERROR_QUIET)
+    IF(_RUBY_SUCCESS OR NOT _RUBY_OUTPUT)
+      EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['${RBVAR}']"
+        RESULT_VARIABLE _RUBY_SUCCESS
+        OUTPUT_VARIABLE _RUBY_OUTPUT
+        ERROR_QUIET)
+    ENDIF(_RUBY_SUCCESS OR NOT _RUBY_OUTPUT)
+    SET(${OUTVAR} "${_RUBY_OUTPUT}" PARENT_SCOPE)
+  ENDFUNCTION(_RUBY_CONFIG_VAR)
 
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['MINOR']"
-      OUTPUT_VARIABLE RUBY_VERSION_MINOR)
 
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['TEENY']"
-      OUTPUT_VARIABLE RUBY_VERSION_PATCH)
+  # query the ruby version
+   _RUBY_CONFIG_VAR("MAJOR" RUBY_VERSION_MAJOR)
+   _RUBY_CONFIG_VAR("MINOR" RUBY_VERSION_MINOR)
+   _RUBY_CONFIG_VAR("TEENY" RUBY_VERSION_PATCH)
 
    # query the different directories
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['archdir']"
-      OUTPUT_VARIABLE RUBY_ARCH_DIR)
-
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['arch']"
-      OUTPUT_VARIABLE RUBY_ARCH)
-
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['rubyhdrdir']"
-      OUTPUT_VARIABLE RUBY_HDR_DIR)
-
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['libdir']"
-      OUTPUT_VARIABLE RUBY_POSSIBLE_LIB_DIR)
-
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['rubylibdir']"
-      OUTPUT_VARIABLE RUBY_RUBY_LIB_DIR)
+   _RUBY_CONFIG_VAR("archdir" RUBY_ARCH_DIR)
+   _RUBY_CONFIG_VAR("arch" RUBY_ARCH)
+   _RUBY_CONFIG_VAR("rubyhdrdir" RUBY_HDR_DIR)
+   _RUBY_CONFIG_VAR("libdir" RUBY_POSSIBLE_LIB_DIR)
+   _RUBY_CONFIG_VAR("rubylibdir" RUBY_RUBY_LIB_DIR)
 
    # site_ruby
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['sitearchdir']"
-      OUTPUT_VARIABLE RUBY_SITEARCH_DIR)
-
-   EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['sitelibdir']"
-      OUTPUT_VARIABLE RUBY_SITELIB_DIR)
+   _RUBY_CONFIG_VAR("sitearchdir" RUBY_SITEARCH_DIR)
+   _RUBY_CONFIG_VAR("sitelibdir" RUBY_SITELIB_DIR)
 
    # vendor_ruby available ?
    EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r vendor-specific -e "print 'true'"
       OUTPUT_VARIABLE RUBY_HAS_VENDOR_RUBY  ERROR_QUIET)
 
    IF(RUBY_HAS_VENDOR_RUBY)
-      EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['vendorlibdir']"
-         OUTPUT_VARIABLE RUBY_VENDORLIB_DIR)
-
-      EXECUTE_PROCESS(COMMAND ${RUBY_EXECUTABLE} -r rbconfig -e "print Config::CONFIG['vendorarchdir']"
-         OUTPUT_VARIABLE RUBY_VENDORARCH_DIR)
+      _RUBY_CONFIG_VAR("vendorlibdir" RUBY_VENDORLIB_DIR)
+      _RUBY_CONFIG_VAR("vendorarchdir" RUBY_VENDORARCH_DIR)
    ENDIF(RUBY_HAS_VENDOR_RUBY)
 
    # save the results in the cache so we don't have to run ruby the next time again