uclibc: clean-up test suite build command

Starting from uClibc 0.9.32 "test_compile" target builds tests flawlessly.
For 0.9.31 it lead to build failure, but now when AVR32 support was dropped
I think this change worth applying.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>