[MIPS] Temporarily disable Mips shared-textrel errors

Clang++ for Mips and Mips64 generates read-only exception unwind
tables that trigger DT_TEXTREL warnings at link time.  Until Clang
is fixed, ignore those performance warnings instead of failing the build.

With this patch, Mips clang++ can be (optionally) used when building
libdeqp.

NDK's Mips llvm has been using an alternate temporary fix, marking the
.gcc_exception_table section as read-write for Mips only:
   https://android-review.googlesource.com/#/c/119660/

A permanent fix using a read-only exception table is pending upstream:
   http://reviews.llvm.org/D9669

Change-Id: Ie0cd7da398acbe45dbe39adc251e7fd5b5ca1445