[PATCH] Version info mixes up host and target platform when cross-compiling

I tried running PostgreSQL on the ARM64 (aka AArch64) emulator and
noticed that the version() string mixes up the host and target
architecture.

Before:
PostgreSQL 9.3devel on x86_64-pc-linux-gnu, compiled by
aarch64-linux-gnu-gcc-4.7 (Ubuntu/Linaro 4.7.2-21ubuntu3) 4.7.2, 64-bit

Now:
PostgreSQL 9.3devel on aarch64-linux-gnu-gcc-4.7 (Ubuntu/Linaro
4.7.2-21ubuntu3) 4.7.2, compiled by x86_64-pc-linux-gnu, 64-bit

In other news, I can confirm that PostgreSQL git HEAD works and passes
all tests on AArch64 on Ubuntu Raring. The tests took 52 minutes to
run in the emulator, but I got there. :)

Obviously native spinlock code is still missing. There are no shipping
processors yet so we have some time.

Regards,
Marti