Solaris cc compiler on amd: PostgreSQL does not have native spinlock support on this platform

Hello,
I'm trying to compile postgresql and I got this message telling me
to inform you:

"../../../../src/include/storage/s_lock.h", line 806: #error: PostgreSQL
does not have native spinlock support on this platform. To continue the
compilation, rerun configure using --disable-spinlocks. However,
performance will be poor. Please report this to pgsql-bugs(at)postgresql(dot)org(dot)

This is the configure line i used:
MAKE=gmake CC=/opt/SUNWspro/bin/cc CFLAGS="-xtarget=opteron
-xarch=amd64" CXX=/opt/SUNWspro/bin/CC CXXFLAGS="-xtarget=opteron
-xarch=amd64" LDFLAGS="-xtarget=opteron -xarch=amd64" ./configure
--without-readline

If i try this configuration command instead:
MAKE=gmake CC=/opt/SUNWspro/bin/cc CFLAGS="-fast"
CXX=/opt/SUNWspro/bin/CC CXXFLAGS="-fast" LDFLAGS="-fast" ./configure
--without-readline

It compiles but then i get a 32 bit executable which is not what i want.

This is on a solaris 10 with amd processor using the sun forte 11 compilers.

Are there any fix for this?

Thanks.