db.pg: improve support on OpenBSD (#26316)

Author: lcheylus

vlib/db/pg/README.md

@@ -39,7 +39,7 @@ brew services start postgresql
 gem install pg -- --with-pg-config=/opt/local/lib/postgresql[version number]/bin/pg_config
 ```
 
-## Installing libpq-dev or its equivalent for your OS:
+## Installing libpq-dev or its equivalent for your OS
 
 **Ubuntu/Debian**: `sudo apt install libpq-dev`
 
@@ -49,6 +49,8 @@ gem install pg -- --with-pg-config=/opt/local/lib/postgresql[version number]/bin
 
 **ArchLinux**: `pacman -S postgresql-libs`
 
+**OpenBSD**: `pkg_add postgresql-client`
+
 **Windows**:
 
 ```

vlib/db/pg/pg.c.v

@@ -31,6 +31,9 @@ $if $pkgconfig('libpq') {
 
 	#flag freebsd -I/usr/local/include
 	#flag freebsd -L/usr/local/lib
+
+	#flag openbsd -I/usr/local/include/postgresql
+	#flag openbsd -L/usr/local/lib
 }
 
 $if cross_compile ? && linux {