recipes: Enable nativesdk for gperf, unifdef, gi-docgen and its dependencies

I'm building a SDK (bitbake task: populate_sdk) for WPE/WebKit
development [1] and I need the tools below to be extended with the class
nativesdk. They work fine on the SDK after this change.

The needs are because:

1) gperf and unifdef are required by the WebKit build system at build
   time.

2) gi-docgen is required by the WebKit build system when CMake option
   'ENABLE_DOCUMENTATION' is enabled, and gi-docgen itself depends on
   the following python modules that also need to enable nativesdk:
   python3-markdown, python3-smartypants and python3-typogrify

[1]
See:
 - https://github.com/Igalia/meta-webkit/pull/436
 - https://bugs.webkit.org/show_bug.cgi?id=249604

(From OE-Core rev: 6cb38fd632a161bea7b9a04de400d8be8d565b07)

Signed-off-by: Carlos Alberto Lopez Perez <clopez@igalia.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/unifdef/unifdef_2.12.bb

@@ -18,4 +18,4 @@ do_install() {
 	oe_runmake install DESTDIR=${D} prefix=${prefix}
 }
 
-BBCLASSEXTEND = "native"
+BBCLASSEXTEND = "native nativesdk"