MakeMakefile#try_const

try_const(const, headers = nil, opt = "", &b)

# File tmp/rubies/ruby-3.3.0/lib/mkmf.rb, line 1313
  def try_const(const, headers = nil, opt = "", &b)
    const, type = *const
    if try_compile(<<"SRC", opt, &b)
#{cpp_include(headers)}
/*top*/
typedef #{type || 'int'} conftest_type;
conftest_type conftestval = #{type ? '' : '(int)'}#{const};
SRC
      $defs.push(format("-DHAVE_CONST_%s", const.tr_cpp))
      true
    else
      false
    end
  end

Returns whether or not the constant const is defined.