Fix an infinite loop while searching for libmysqlclient when mysql_config is not found

Generally improve the code for trying the extra runtime libraries

Author: sodabrew

ext/mysql2/extconf.rb

@@ -73,15 +73,22 @@ def asplode lib
   rpath_dir = libs
 else
   inc, lib = dir_config('mysql', '/usr/local')
-  libs = ['m', 'z', 'socket', 'nsl', 'mygcc']
-  found = false
-  while not find_library('mysqlclient', 'mysql_query', lib, "#{lib}/mysql") do
-    exit 1 if libs.empty?
-    found ||= have_library(libs.shift)
+  unless find_library('mysqlclient', 'mysql_query', lib, "#{lib}/mysql")
+    found = false
+    # For some systems and some versions of libmysqlclient, there were extra
+    # libraries needed to link. Try each typical extra library, add it to the
+    # global compile flags, and see if that allows us to link libmysqlclient.
+    warn "-----\nlibmysqlclient is missing. Trying again with extra runtime libraries...\n-----"
+
+    %w{ m z socket nsl mygcc }.each do |extra_lib|
+      if have_library(extra_lib) && find_library('mysqlclient', 'mysql_query', lib, "#{lib}/mysql")
+        found = true
+        break
+      end
+    end
+    asplode('libmysqlclient') unless found
   end
 
-  asplode("mysql client") unless found
-
   rpath_dir = lib
 end