[test-release.sh] Add -no-libunwind to disable it on targets that don't support it.

[dsanders]

Summary

Mips doesn't implement unw_getcontext() or libunwind::Registers_*::jumpto() yet
so we must disable libunwind for this release.

[hans]

lgtm

utils/release/test-release.sh

 Triple=""
 use_gzip="no"
 do_checkout="yes"
 do_debug="no"
 do_asserts="no"
 do_compare="yes"
 do_rt="yes"
 do_libs="yes"
+do_libunwind="yes"
 do_test_suite="yes"
 BuildDir="`pwd`"
 use_autoconf="no"
 ExtraConfigureFlags=""
 
 function usage() {
     echo "usage: `basename $0` -release X.Y.Z -rc NUM [OPTIONS]"
     echo ""
     echo " -release X.Y.Z       The release version to test."
     echo " -rc NUM              The pre-release candidate number."
     echo " -final               The final release candidate."
     echo " -triple TRIPLE       The target triple for this machine."
     echo " -j NUM               Number of compile jobs to run. [default: 3]"
     echo " -build-dir DIR       Directory to perform testing in. [default: pwd]"
     echo " -no-checkout         Don't checkout the sources from SVN."
     echo " -test-debug          Test the debug build. [default: no]"
     echo " -test-asserts        Test with asserts on. [default: no]"
     echo " -no-compare-files    Don't test that phase 2 and 3 files are identical."
     echo " -use-gzip            Use gzip instead of xz."
     echo " -configure-flags FLAGS  Extra flags to pass to the configure step."
     echo " -use-autoconf        Use autoconf instead of cmake"
     echo " -no-rt               Disable check-out & build Compiler-RT"
     echo " -no-libs             Disable check-out & build libcxx/libcxxabi/libunwind"
+    echo " -no-libunwind        Disable check-out & build libunwind"
     echo " -no-test-suite       Disable check-out & build test-suite"
 }
 
 if [ `uname -s` = "Darwin" ]; then
   # compiler-rt doesn't yet build with CMake on Darwin.
   use_autoconf="yes"
 fi
 
case $1 in
             use_autoconf="yes"
             ;;
         -no-rt )
             do_rt="no"
             ;;
         -no-libs )
             do_libs="no"
             ;;
+        -no-libunwind )
+            do_libunwind="no"
+            ;;
         -no-test-suite )
             do_test_suite="no"
             ;;
         -help | --help | -h | --h | -\? )
             usage
             exit 0
             ;;
         * )

 fi
 
 # Projects list
 projects="llvm cfe clang-tools-extra"
 if [ $do_rt = "yes" ]; then
   projects="$projects compiler-rt"
 fi
 if [ $do_libs = "yes" ]; then
-  projects="$projects libcxx libcxxabi libunwind"
+  projects="$projects libcxx libcxxabi"
+  if [ $do_libunwind = "yes" ]; then
+    projects="$projects libunwind"
+  fi
 fi
 if [ $do_test_suite = "yes" ]; then
   projects="$projects test-suite"
 fi
 
 # Go to the build directory (may be different from CWD)
 BuildDir=$BuildDir/$RC
 mkdir -p $BuildDir