* Sync upb

https://github.com/protocolbuffers/upb/pull/209

* Update upb

https://github.com/protocolbuffers/upb/pull/210

* Sync upb

* https://github.com/protocolbuffers/upb/pull/208

* Fix php c extension compiling

Don't use macros defined by upb

* Update ruby conformance failure list

We were creating a map decoding frame when starting the *map*,
but clearing the GC slot when finishing each *map entry*.  This
means that the decoding frame could be collected in the meantime.

This fixes https://github.com/protocolbuffers/protobuf/issues/6532.

* Rolled forward again with "Updated upb from defcleanup branch..."

Revert "Revert "Updated upb from defcleanup branch and modified Ruby to use it (#5539)" (#5848)"

This reverts commit 1568deab.

* A few more merge fixes.

* Updated for defcleanup2 branch.

* Fixed upb to define upb_decode().

* Fixed names of nested messages.

* Revert submodule.

* Set -std=gnu90 and fixed warnings/errors.

Some of our Kokoro tests seem to run with this level of warnings,
and the source strives to be gnu90 compatible.  Enforcing it for
every build removes the possibility of some errors showing up in
Kokoro/Travis tests only.

* Fixed remaining warnings with gnu90 mode.

I tried to match warning flags with what Ruby appears to do
in our Kokoro tests.

* Initialize values registered by rb_gc_register_address().

* Fixed subtle GC bug.

We need to initialize this marked value before creating the instance.

* Truly fix the GC bug.

* Updated upb for mktime() fix.

* Removed XOPEN_SOURCE as we are not using strptime().

* Removed fixed tests from the conformance failure list for Ruby.

* Fixed memory error related to oneof def names.

* Picked up new upb changes re: JSON printing.

* Uncomment concurrent decoding test.

Prior to this CL, creating an empty message object would create
two empty string objects for every declared field.  First we
created a unique string object for the field's default.  Then
we created yet another string object when we assigned the
default value into the message: we called #encode to ensure
that the string would have the correct encoding and be frozen.

I optimized these unnecessary objects away with two fixes:

1. Memoize the empty string so that we don't create a new empty
   string for every field's default.
2. If we are assigning a string to a message object, avoid creating
   a new string if the assigned string has the correct encoding and
   is already frozen.

* support hashes for struct initalizers

* convert hash keys to string

* update tests

* add extra asserts

* Change int64 json encoding to be string for php and ruby

* Fix ruby test

* Sync upb change

value_field_typeclass should be a enum module, not EnumDescriptor
object.

Also expanding tests for enum valued maps.

Fixes #4580
Signed-off-by: Sorah Fukumori <her@sorah.jp>

In general, I think it will help us to debug issues if we have less C
code and more Ruby code.  This method can be implemented in pure Ruby,
so this commit converts it to pure Ruby.

* Custom mktime to fix issue on mac

* Remove succeeded tests from failure list

* add wrapper type helpers

* add check for _as_value suffix

* add implicit time conversion

* add duration

* add init test

* more tests

* add type check and alternative c type check

* add rational and bigdecimal

* use rb_obj_is_kind_of

* use native time check

* chain implicit conversions

* remove unused variable

* Allow bytes field to be longer than 16000 bytes

* Remove empty line

* Replace strptime with custom implementation

* Fix ruby strptime

* Fix test

* Fix ruby conformance test

* Use mktime

* Remove EmptyFieldMask from failed conformance test list

* Add conformance test for nested listvalue

* Fix upb for parsing repeated Value/ListValue

* Add failed repeated ListValue conformance test into php failure list

* Encode empty ListValue

* Update mac ruby conformance failure list

* add check for overflow

* de-nestify

* break long lines

This reverts commit 37581380.

* add frozen checks

* Use rb_check_frozen

* Correct assertion on frozen error message

The second argument for the method assert_raise is the message
to show when the assertion fails. It does not check the error
object's message.
Add an additional assertion that does check the error's message.

* do frozen check first

* example with extra enum method

* update expected test output

* slight simplification

* add test for generated enum helpers

* move const helpers to c extension

* more explicit test

* more explicit test

* indent

* add foo test

* add check for _const suffix

* add check for overflow

* de-nestify

* break long lines