postgresql: add missing librt dependency

fixes build error with uclibc

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>

libs/postgresql/Makefile

@@ -42,7 +42,7 @@ endef
 define Package/pgsql-cli
   SECTION:=utils
   CATEGORY:=Utilities
-  DEPENDS:=+libpq
+  DEPENDS:=+libpq @USE_UCLIBC:+librt
   TITLE:=Command Line Interface (CLI) to PostgreSQL databases
   URL:=http://www.postgresql.org/
   SUBMENU:=database
@@ -55,7 +55,7 @@ endef
 define Package/pgsql-server
   SECTION:=utils
   CATEGORY:=Utilities
-  DEPENDS:=+libpq
+  DEPENDS:=+libpq @USE_UCLIBC:+librt
   TITLE:=PostgreSQL databases Server
   URL:=http://www.postgresql.org/
   SUBMENU:=database