dev-util/watchman: disable automagic dev-cpp/folly (non-existent usage)

Currently testing out folly for a future bump but the old version of watchman
will pick up and try to use folly if it's installed. But it won't build anyway.

Signed-off-by: Sam James <sam@gentoo.org>

dev-util/watchman/watchman-4.9.0.ebuild

@@ -1,4 +1,4 @@
-# Copyright 2020-2021 Gentoo Authors
+# Copyright 2020-2022 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=7
@@ -36,6 +36,7 @@ src_configure() {
 	econf \
 		--enable-lenient \
 		--disable-statedir \
+		--disable-cppclient \
 		--without-python \
 		$(use_with pcre)
 }