Rails pg gem '0.14.1' on Mac fails and solution

pg.c: In function ‘Init_pg_ext’:
pg.c:384: error: ‘PQPING_OK’ undeclared (first use in this function)
pg.c:384: error: (Each undeclared identifier is reported only once
pg.c:384: error: for each function it appears in.)
pg.c:386: error: ‘PQPING_REJECT’ undeclared (first use in this function)
pg.c:388: error: ‘PQPING_NO_RESPONSE’ undeclared (first use in this function)
pg.c:390: error: ‘PQPING_NO_ATTEMPT’ undeclared (first use in this function)
make: *** [pg.o] Error 1

Solution:
env ARCHFLAGS="-arch x86_64" gem install pg -- --with-pg-config=/Library/PostgreSQL/9.2/bin/pg_config

EDIT :
If you dont know where your pg_config is. Assume you are on Linux/Mac system, using the command 'find' should help

find / -name pg_config