    # File lib/phusion_passenger/platform_info/compiler.rb, line 103
            def self.portability_cflags
                    flags = ["-D_REENTRANT -I/usr/local/include"]

                    # Google SparseHash flags.
                    # Figure out header for hash function object and its namespace.
                    # Based on stl_hash.m4 and stl_hash_fun.m4 in the Google SparseHash sources.
                    hash_namespace = nil
                    ok = false
                    ['__gnu_cxx', '', 'std', 'stdext'].each do |namespace|
                            ['ext/hash_map', 'hash_map'].each do |hash_map_header|
                                    ok = try_compile(:cxx, %Q{
                                            #include <#{hash_map_header}>
                                            int
                                            main() {
                                                    #{namespace}::hash_map<int, int> m;
                                                    return 0;
                                            }
                                    })
                                    if ok
                                            hash_namespace = namespace
                                            flags << "-DHASH_NAMESPACE=\"#{namespace}\""
                                    end
                            end
                            break if ok
                    end
                    ['ext/hash_fun.h', 'functional', 'tr1/functional',
                     'ext/stl_hash_fun.h', 'hash_fun.h', 'stl_hash_fun.h',
                     'stl/_hash_fun.h'].each do |hash_function_header|
                            ok = try_compile(:cxx, %Q{
                                    #include <#{hash_function_header}>
                                    int
                                    main() {
                                            #{hash_namespace}::hash<int>()(5);
                                            return 0;
                                    }
                            })
                            if ok
                                    flags << "-DHASH_FUN_H=\"<#{hash_function_header}>\""
                                    break
                            end
                    end

                    if RUBY_PLATFORM =~ /solaris/
                            flags << '-pthreads'
                            if RUBY_PLATFORM =~ /solaris2.11/
                                    # skip the _XOPEN_SOURCE and _XPG4_2 definitions in later versions of Solaris / OpenIndiana
                                    flags << '-D__EXTENSIONS__ -D__SOLARIS__ -D_FILE_OFFSET_BITS=64'
                            else
                                    flags << '-D_XOPEN_SOURCE=500 -D_XPG4_2 -D__EXTENSIONS__ -D__SOLARIS__ -D_FILE_OFFSET_BITS=64'
                                    flags << '-D__SOLARIS9__ -DBOOST__STDC_CONSTANT_MACROS_DEFINED' if RUBY_PLATFORM =~ /solaris2.9/
                            end
                            flags << '-DBOOST_HAS_STDINT_H' unless RUBY_PLATFORM =~ /solaris2.9/
                            flags << '-mcpu=ultrasparc' if RUBY_PLATFORM =~ /sparc/
                    elsif RUBY_PLATFORM =~ /openbsd/
                            flags << '-DBOOST_HAS_STDINT_H -D_GLIBCPP__PTHREADS'
                    elsif RUBY_PLATFORM =~ /aix/
                            flags << '-pthread'
                            flags << '-DOXT_DISABLE_BACKTRACES'
                    elsif RUBY_PLATFORM =~ /(sparc-linux|arm-linux|^arm.*-linux|sh4-linux)/
                            # http://code.google.com/p/phusion-passenger/issues/detail?id=200
                            # http://groups.google.com/group/phusion-passenger/t/6b904a962ee28e5c
                            # http://groups.google.com/group/phusion-passenger/browse_thread/thread/aad4bd9d8d200561
                            flags << '-DBOOST_SP_USE_PTHREADS'
                    end

                    flags << '-DHAS_ALLOCA_H' if has_alloca_h?
                    flags << '-DHAS_SFENCE' if supports_sfence_instruction?
                    flags << '-DHAS_LFENCE' if supports_lfence_instruction?

                    return flags.compact.join(" ").strip
            end