Fix broken compilation with Ruby interpreter compiled with XCode 14

XCode 14 warns if the `-undefined dynamic_lookup` linker option is
used. As a result, the `configure` script for the Ruby interpreter
disables these flags, causing building the native gem to fail with
undefined symbols:

```
compiling encoder.c
encoder.c:307:14: warning: unused function 'rb_cBignum_ffi_yajl' [-Wunused-function]
static VALUE rb_cBignum_ffi_yajl(VALUE self, VALUE rb_yajl_gen, VALUE state) {
             ^
1 warning generated.
linking shared-object ffi_yajl/ext/encoder.bundle
Undefined symbols for architecture arm64:
  "_yajl_gen_alloc", referenced from:
      _mEncoder_do_yajl_encode in encoder.o
  "_yajl_gen_array_close", referenced from:
      _gen_array_close in encoder.o
  "_yajl_gen_array_open", referenced from:
      _gen_array_open in encoder.o
  "_yajl_gen_bool", referenced from:
      _gen_true in encoder.o
      _gen_false in encoder.o
  "_yajl_gen_config", referenced from:
      _mEncoder_do_yajl_encode in encoder.o
  "_yajl_gen_free", referenced from:
      _mEncoder_do_yajl_encode in encoder.o
  "_yajl_gen_get_buf", referenced from:
      _mEncoder_do_yajl_encode in encoder.o
  "_yajl_gen_map_close", referenced from:
      _gen_map_close in encoder.o
  "_yajl_gen_map_open", referenced from:
      _gen_map_open in encoder.o
  "_yajl_gen_null", referenced from:
      _gen_null in encoder.o
  "_yajl_gen_number", referenced from:
      _gen_number in encoder.o
  "_yajl_gen_string", referenced from:
      _gen_cstring in encoder.o
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [encoder.bundle] Error 1
```

To fix this, we can explicitly list the symbols that will be
dynamically looked up and use that in the `-U` linker option to
specify that it is okay for that symbol to have no definition.

Relates to ruby/ruby#6193

Signed-off-by: Stan Hu <stanhu@gmail.com>

ext/ffi_yajl/ext/dlopen/yajl.sym

@@ -0,0 +1,18 @@
+_yajl_gen_alloc
+_yajl_gen_array_close
+_yajl_gen_array_open
+_yajl_gen_bool
+_yajl_gen_config
+_yajl_gen_free
+_yajl_gen_get_buf
+_yajl_gen_map_close
+_yajl_gen_map_open
+_yajl_gen_null
+_yajl_gen_number
+_yajl_gen_string
+_yajl_alloc
+_yajl_complete_parse
+_yajl_config
+_yajl_free
+_yajl_get_error
+_yajl_parse

ext/ffi_yajl/ext/encoder/extconf.rb

@@ -27,6 +27,27 @@ def windows?
   !!(RUBY_PLATFORM =~ /mswin|mingw|cygwin|windows/)
 end
 
+def macos?
+  !!(RUBY_PLATFORM =~ /darwin/)
+end
+
+def clang?
+  cc_version = `#{RbConfig.expand("$(CC) --version")}`
+  cc_version.match?(/clang/i)
+end
+
+# XCode 14 warns if `-Wl,-undefined dynamic_lookup` is specified, and as
+# a result Ruby interpreters compiled under XCode 14 no longer specify
+# this flag by default in DLDFLAGS. Let's specify the list of dynamic symbols
+# here to avoid compilation failures.
+if clang? && macos?
+  symfile = File.join(__dir__, '../dlopen/yajl.sym')
+  dynamic_symbols = File.readlines(symfile)
+  dynamic_symbols.each do |sym|
+    $DLDFLAGS << " -Wl,-U,#{sym.strip}"
+  end
+end
+
 if windows?
   # include our libyajldll.a definitions on windows in the libyajl2 gem
   $libs = "#{$libs} -lyajldll"

ext/ffi_yajl/ext/parser/extconf.rb

@@ -27,6 +27,27 @@ def windows?
   !!(RUBY_PLATFORM =~ /mswin|mingw|cygwin|windows/)
 end
 
+def macos?
+  !!(RUBY_PLATFORM =~ /darwin/)
+end
+
+def clang?
+  cc_version = `#{RbConfig.expand("$(CC) --version")}`
+  cc_version.match?(/clang/i)
+end
+
+# XCode 14 warns if `-Wl,-undefined dynamic_lookup` is specified, and as
+# a result Ruby interpreters compiled under XCode 14 no longer specify
+# this flag by default in DLDFLAGS. Let's specify the list of dynamic symbols
+# here to avoid compilation failures.
+if clang? && macos?
+  symfile = File.join(__dir__, '../dlopen/yajl.sym')
+  dynamic_symbols = File.readlines(symfile)
+  dynamic_symbols.each do |sym|
+    $DLDFLAGS << " -Wl,-U,#{sym.strip}"
+  end
+end
+
 if windows?
   # include our libyajldll.a definitions on windows in the libyajl2 gem
   $libs = "#{$libs} -lyajldll"