strace: Disable for MIPS when using a uClibc toolchain

A change introduced in strace-4.9 makes it incompatible with MIPS
architecture when using a uClibc toolchain. This is the failure:

signal.c: In function 'printsiginfo':
signal.c:453:9: error: 'siginfo_t' has no member named 'si_timerid'
      sip->si_timerid, sip->si_overrun);
	 ^
signal.c:453:26: error: 'siginfo_t' has no member named 'si_overrun'
      sip->si_timerid, sip->si_overrun);

uClibc needs to be patched in order to fix this problem. In the meantime
we disable strace for MIPS when using a uClibc toolchain.

Fixes:

  http://autobuild.buildroot.net/results/91c/91c0413e755c365332bc15d1d69ab3d6160ae78c/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>