pixman: unbreak on nios codesourcery 2014.05

Fixes
http://autobuild.buildroot.net/results/ec3/ec31257a66583ca69bbad5ecfedb4c25b85268ee/
http://autobuild.buildroot.net/results/b24/b241ef7b7283efd92028d98355f268d93a12ffdd/
http://autobuild.buildroot.net/results/36c/36cc9386747854b632ec4e22bed8f32a0e2eec32/
http://autobuild.buildroot.net/results/b8a/b8a2de871eec249d03744fcd4ea6b5d3d1b01bd5/



And many others.

The toolchain gets confused about TLS access through the GOT (PIC), so
disable TLS support in pixman.

The error from the assembler is:
movhi	r4, %got_hiadj(%tls_ldo(fast_path_cache))
{standard input}:172: Error: bad expression

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>