* ext/date/extconf.rb: try_cflags("-std=iso9899:1999") [Bug #10906]
ruby itself (including numeric.c) is built with strict compile
options including -std=iso9899:1999, but ext/date is not.
By the way -std=iso9899:1999 is not only a warning option but also
changes behavior like MACRO definitions for example INFINITY.
gcc on Solaris affect this.
merge revision(s) 50104,50105: [Backport #10906]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@52645 b2dd03c8-39d4-4d8f-98ff-823fe69b080e