[CMake] Workaround for PR24222: don't fail if we can't target COMPILER_RT_TEST_TARGET_TRIPLE unless it was explicitly set.

[samsonov]

Summary

Although we assume that we can always target host triple, relax
this check to avoid failing at configure-time for cases when we are
not able to correctly infer/verify host triple for some reasons.

See http://llvm.org/bugs/show_bug.cgi?id=24222 for more details.

[hans]

lgtm, thanks.

It would be nice if we could fix the other half of PR24222 too though, where clang doesn't define i686.

CMakeLists.txt

 
 # Tests using XFAIL use the first value in COMPILER_RT_TEST_TARGET_TRIPLE
 set(COMPILER_RT_TEST_TARGET_TRIPLE ${TARGET_TRIPLE} CACHE STRING
     "Default triple for cross-compiled executables")
 string(REPLACE "-" ";" TARGET_TRIPLE_LIST ${COMPILER_RT_TEST_TARGET_TRIPLE})
 list(GET TARGET_TRIPLE_LIST 0 COMPILER_RT_TEST_TARGET_ARCH)
 list(GET TARGET_TRIPLE_LIST 1 COMPILER_RT_TEST_TARGET_OS)
 list(GET TARGET_TRIPLE_LIST 2 COMPILER_RT_TEST_TARGET_ABI)
+# Determine if test target triple is specified explicitly, and doesn't match the
+# default.
+if(NOT COMPILER_RT_TEST_TARGET_TRIPLE STREQUAL TARGET_TRIPLE)
+  set(COMPILER_RT_HAS_EXPLICIT_TEST_TARGET_TRIPLE TRUE)
+else()
+  set(COMPILER_RT_HAS_EXPLICIT_TEST_TARGET_TRIPLE FALSE)
+endif()
 
 if ("${COMPILER_RT_TEST_TARGET_ABI}" STREQUAL "androideabi")
   set(ANDROID 1)
 endif()
 
 string(TOLOWER ${CMAKE_SYSTEM_NAME} COMPILER_RT_OS_DIR)
 set(COMPILER_RT_LIBRARY_OUTPUT_DIR
   ${COMPILER_RT_OUTPUT_DIR}/lib/${COMPILER_RT_OS_DIR})

cmake/config-ix.cmake

else()
     set(argstring "${CMAKE_EXE_LINKER_FLAGS} ${argstring}")
     try_compile(CAN_TARGET_${arch} ${CMAKE_BINARY_DIR} ${SIMPLE_SOURCE}
                 COMPILE_DEFINITIONS "${TARGET_${arch}_CFLAGS}"
                 OUTPUT_VARIABLE TARGET_${arch}_OUTPUT
                 CMAKE_FLAGS "-DCMAKE_EXE_LINKER_FLAGS:STRING=${argstring}")
   endif()
   if(${CAN_TARGET_${arch}})
     list(APPEND COMPILER_RT_SUPPORTED_ARCH ${arch})
-  elseif("${COMPILER_RT_TEST_TARGET_ARCH}" MATCHES "${arch}")
+  elseif("${COMPILER_RT_TEST_TARGET_ARCH}" MATCHES "${arch}" AND
+         COMPILER_RT_HAS_EXPLICIT_TEST_TARGET_TRIPLE)
     # Bail out if we cannot target the architecture we plan to test.
     message(FATAL_ERROR "Cannot compile for ${arch}:\n${TARGET_${arch}_OUTPUT}")
   endif()
 endmacro()
 
 # Add $arch as supported with no additional flags.
 macro(add_default_target_arch arch)
   set(TARGET_${arch}_CFLAGS "")