Added explicitly begin-end block for Ruby 2.4.

strscan, ipaddr and some default gems still support Ruby 2.4.

  After this, I extract this CoreAssertions to their repositories.

tool/lib/core_assertions.rb

@@ -781,6 +781,7 @@ eom
       ].find do |c|
         if Process.const_defined?(c)
           [c.to_sym, Process.const_get(c)].find do |clk|
+            begin
               Process.clock_gettime(clk)
             rescue
               # Constants may be defined but not implemented, e.g., mingw.
@@ -789,6 +790,7 @@ eom
             end
           end
         end
+      end
 
       # Expect +seq+ to respond to +first+ and +each+ methods, e.g.,
       # Array, Range, Enumerator::ArithmeticSequence and other