media-gfx/silicon: use := operators for native library deps

Signed-off-by: YOSHIOKA Takuma <lo48576@hard-wi.red>

media-gfx/silicon/silicon-0.5.3.ebuild

@@ -239,11 +239,11 @@ BDEPEND="
 	virtual/pkgconfig
 	${PYTHON_DEPS}"
 DEPEND="
-	dev-libs/oniguruma
-	media-libs/fontconfig
-	media-libs/freetype
-	media-libs/harfbuzz
-	x11-libs/libxcb"
+	dev-libs/oniguruma:=
+	media-libs/fontconfig:=
+	media-libs/freetype:=
+	media-libs/harfbuzz:=
+	x11-libs/libxcb:="
 RDEPEND="${DEPEND}
 	x11-misc/xclip"