postgresql: fix sparc compile issue

Fixes autobuilder compile error:
http://autobuild.buildroot.net/results/f374d3535cf91f139ce80703cd2d0a2be5d3b2b1/



The predefines are wrong:
./output/host/usr/bin/sparc-buildroot-linux-uclibc-gcc -dM -E - </dev/null|grep sparc
#define sparc 1
#define __sparc__ 1
#define __sparc 1
#define __sparc_v8__ 1

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>