Place includedir_server first so pg_config.h has the correct PG_VERSION_NUM

--- a/Makefile.in
+++ b/Makefile.in
@@ -46,7 +46,7 @@ all: \
 	repmgrd
 
 # When in development add -Werror
-PG_CPPFLAGS = -std=gnu89 -I$(includedir_internal) -I$(libpq_srcdir) -Wall -Wmissing-prototypes -Wmissing-declarations $(EXTRA_CFLAGS)
+PG_CPPFLAGS = -std=gnu89 -I$(includedir_server) -I$(includedir_internal) -I$(libpq_srcdir) -Wall -Wmissing-prototypes -Wmissing-declarations $(EXTRA_CFLAGS)
 SHLIB_LINK = $(libpq)
 
 
