Update rdoc for pkg_config() and move :stopdoc: below to enable it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41252 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/mkmf.rb

@@ -1715,8 +1715,6 @@ SRC
     [idir, ldir]
   end
 
-  # :stopdoc:
-
   # Returns compile/link information about an installed library in a
   # tuple of <code>[cflags, ldflags, libs]</code>, by using the
   # command found first in the following commands:
@@ -1730,8 +1728,12 @@ SRC
   #
   # Where {option} is, for instance, <code>--cflags</code>.
   #
+  # The values obtained are appended to +$CFLAGS+, +$LDFLAGS+ and
+  # +$libs+.
+  #
   # If an <code>option</code> argument is given, the config command is
-  # invoked with the option and a stripped output string is returned.
+  # invoked with the option and a stripped output string is returned
+  # without modifying any of the global values mentioned above.
   def pkg_config(pkg, option=nil)
     if pkgconfig = with_config("#{pkg}-config") and find_executable0(pkgconfig)
       # iff package specific config command is given
@@ -1765,6 +1767,8 @@ SRC
     end
   end
 
+  # :stopdoc:
+
   def with_destdir(dir)
     return dir unless $extmk
     dir = dir.sub($dest_prefix_pattern, '')