Fixed build with `conf.enable_cxx_exception`

The problem was manifested by commit 5069fb15.

mrbgems/mruby-bin-mirb/tools/mirb/mirb.c

@@ -18,7 +18,6 @@
 #include <mruby/dump.h>
 #include <mruby/string.h>
 #include <mruby/variable.h>
-#include <mruby/throw.h>
 
 #include <stdlib.h>
 #include <string.h>

mrbgems/mruby-compiler/mrbgem.rake

@@ -5,7 +5,7 @@ MRuby::Gem::Specification.new 'mruby-compiler' do |spec|
 
   lex_def = "#{dir}/core/lex.def"
   core_objs = Dir.glob("#{dir}/core/*.c").map { |f|
-    next nil if build.cxx_exception_enabled? and f =~ /(codegen).c$/
+    next nil if build.cxx_exception_enabled? and f =~ /(codegen|y\.tab)\.c$/
     objfile(f.pathmap("#{build_dir}/core/%n"))
   }.compact
 

src/mruby_core.rake

@@ -4,12 +4,12 @@ MRuby.each_target do
   current_build_dir = "#{build_dir}/#{relative_from_root}"
 
   objs = Dir.glob("#{current_dir}/*.c").map { |f|
-    next nil if cxx_exception_enabled? and f =~ /(error|vm).c$/
+    next nil if cxx_exception_enabled? and f =~ /(error|vm|gc)\.c$/
     objfile(f.pathmap("#{current_build_dir}/%n"))
   }.compact
 
   if cxx_exception_enabled?
-    objs += %w(vm error).map { |v| compile_as_cxx "#{current_dir}/#{v}.c", "#{current_build_dir}/#{v}.cxx" }
+    objs += %w(vm error gc).map { |v| compile_as_cxx "#{current_dir}/#{v}.c", "#{current_build_dir}/#{v}.cxx" }
   end
   self.libmruby_objs << objs