postgresql: Update to version 11.3

postgresql: Update to version 11.3

Version 11.3 is the current stable relase.

Changes between 9.3 and 11.3:
- pg_receivexlog, pg_resetxlog and pg_xlogdump have been replaced with pg_resetwal
- ZIC config variable must be set when cross compiling
- disable systemd support
- ecpg is no longer needed for building
- MAKELEVEL must be set to 0 when called from another makefile
- Setting AC_CONFIG_AUX_DIR([config]) is no longer requried
- Decrease build time by removing unnecessary configure checks

Signed-off-by: Daniel Danzberger <daniel@dd-wrt.com>