[PATCH] Don't use non blocking pipes for RUBY_CRASH_REPORT

	[Bug #21703]

	RUBY_CRASH_REPORT does not work in some cases when shelling out on Linux.
	For example, given the following shell script dump.sh:

	    #!/usr/bin/env bash
	    cat > /tmp/crash

	And we see it fails like this:

	    $ RUBY_CRASH_REPORT="|dump.sh" ruby -rfiddle -e "Fiddle::Pointer.new(1, 10)[0]"
	    cat: -: Resource temporarily unavailable

https://github.com/sampersand/blog/blob/master/the%20-s%20flag.md#the-segfault

We have name fragmentation for this feature, including "shared GC",
"modular GC", and "external GC". This commit standardizes the feature
name to "modular GC" and the implementation to "GC library".

This will add +MOD_GC to the version string and Ruby description when
Ruby is compiled with shared gc support.

When shared GC support is compiled in and a GC module has been loaded
using RUBY_GC_LIBRARY, the version string will include the name of
the currently active GC as reported by the rb_gc_active_gc_name function
in the form

+MOD_GC[gc_name]

[Feature #20794]

to show unused block warning strictly.

```ruby
class C
  def f = nil
end

class D
  def f = yield
end

[C.new, D.new].each{|obj| obj.f{}}
```

In this case, `D#f` accepts a block. However `C#f` doesn't
accept a block. There are some cases passing a block with
`obj.f{}` where `obj` is `C` or `D`. To avoid warnings on
such cases, "unused block warning" will be warned only if
there is not same name which accepts a block.
On the above example, `C.new.f{}` doesn't show any warnings
because there is a same name `D#f` which accepts a block.

We call this default behavior as "relax mode".

`strict_unused_block` new warning category changes from
"relax mode" to "strict mode", we don't check same name
methods and `C.new.f{}` will be warned.

[Feature #15554]

The temporary directory is the second argument.

[Feature #20205]

The warning now suggests running with --debug-frozen-string-literal:

```
test.rb:3: warning: literal string will be frozen in the future (run with --debug-frozen-string-literal for more information)
```

When using --debug-frozen-string-literal, the location where the string
was created is shown:

```
test.rb:3: warning: literal string will be frozen in the future
test.rb:1: info: the string was created here
```

When resurrecting strings and debug mode is not enabled, the overhead is a simple FL_TEST_RAW.
When mutating chilled strings and deprecation warnings are not enabled,
the overhead is a simple warning category enabled check.

Co-authored-by: Jean Boussier <byroot@ruby-lang.org>
Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>
Co-authored-by: Jean Boussier <byroot@ruby-lang.org>