implement ConfigureOp#check_cxx_header

build_tests/configure/check_cxx_header_failure.rb

@@ -0,0 +1,3 @@
+configure do
+  check_cxx_header "not___found.h"
+end

build_tests/configure/check_cxx_header_no_fail.rb

@@ -0,0 +1,3 @@
+configure do
+  check_cxx_header "not___found.h", fail: false
+end

build_tests/configure/check_cxx_header_success.rb

@@ -0,0 +1,3 @@
+configure do
+  check_cxx_header "string.h"
+end