Fix bug with multi-architecture xray build

[george.karpenkov]

Summary

I think this will fix a failure in http://lab.llvm.org:8011/builders/clang-cmake-mips/builds/4941
Simon, do you think you could test?

[george.karpenkov]

@kcc I think this should be OK to push now, right? Unfortunately, I can not test multi-arch builds on my Linux machine, but the error seems quite obvious.

[kcc]

Sorry, I don't own the xray code.

[george.karpenkov]

@kcc I've introduced the bug in the CMake refactoring commit

[kcc]

LGTM

[sdardis]

Yeah, it works here. Thanks.

compiler-rt/trunk/lib/xray/tests/CMakeLists.txt

 include_directories(..)
 
 add_custom_target(XRayUnitTests)
 set_target_properties(XRayUnitTests PROPERTIES FOLDER "XRay unittests")
 
 set(XRAY_UNITTEST_CFLAGS
   ${XRAY_CFLAGS}
   ${COMPILER_RT_UNITTEST_CFLAGS}
   ${COMPILER_RT_GTEST_CFLAGS}
   -I${COMPILER_RT_SOURCE_DIR}/include
   -I${COMPILER_RT_SOURCE_DIR}/lib/xray
   -I${COMPILER_RT_SOURCE_DIR}/lib)
 
 macro(add_xray_unittest testname)
   set(XRAY_TEST_ARCH ${XRAY_SUPPORTED_ARCH})
   cmake_parse_arguments(TEST "" "" "SOURCES;HEADERS" ${ARGN})
-  set(TEST_OBJECTS)
   # FIXME: Figure out how to run even just the unit tests on APPLE.
   if(UNIX AND NOT APPLE)
     foreach(arch ${XRAY_TEST_ARCH})
+      set(TEST_OBJECTS)
       generate_compiler_rt_tests(TEST_OBJECTS
         XRayUnitTests "${testname}-${arch}" "${arch}"
         SOURCES ${TEST_SOURCES} ${COMPILER_RT_GTEST_SOURCE}
         DEPS gtest_main xray
         CFLAGS ${XRAY_UNITTEST_CFLAGS}
         LINK_FLAGS
           -lstdc++ -lm ${CMAKE_THREAD_LIBS_INIT}
           -lpthread