Index: lib/fuzzer/tests/CMakeLists.txt
===================================================================
--- lib/fuzzer/tests/CMakeLists.txt
+++ lib/fuzzer/tests/CMakeLists.txt
@@ -26,36 +26,38 @@
   list(APPEND LIBFUZZER_UNITTEST_CFLAGS -nostdinc++ -D_LIBCPP_ABI_VERSION=Fuzzer)
 endif()
 
-# libFuzzer unit tests are only run on the host machine.
-set(arch "x86_64")
-
-set(LIBFUZZER_TEST_RUNTIME RTFuzzerTest.${arch})
-if(APPLE)
-  set(LIBFUZZER_TEST_RUNTIME_OBJECTS
-    $<TARGET_OBJECTS:RTfuzzer.osx>)
-else()
-  set(LIBFUZZER_TEST_RUNTIME_OBJECTS
-    $<TARGET_OBJECTS:RTfuzzer.${arch}>)
-endif()
-add_library(${LIBFUZZER_TEST_RUNTIME} STATIC
-  ${LIBFUZZER_TEST_RUNTIME_OBJECTS})
-set_target_properties(${LIBFUZZER_TEST_RUNTIME} PROPERTIES
-  ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-  FOLDER "Compiler-RT Runtime tests")
-
-if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH)
-  set(LIBFUZZER_TEST_RUNTIME_DEPS libcxx_fuzzer_${arch}-build)
-  set(LIBFUZZER_TEST_RUNTIME_CFLAGS -isystem ${COMPILER_RT_LIBCXX_PATH}/include)
-  set(LIBFUZZER_TEST_RUNTIME_LINK_FLAGS ${LIBCXX_${arch}_PREFIX}/lib/libc++.a)
+if(COMPILER_RT_DEFAULT_TARGET_ARCH IN_LIST FUZZER_SUPPORTED_ARCH)
+  # libFuzzer unit tests are only run on the host machine.
+  set(arch ${COMPILER_RT_DEFAULT_TARGET_ARCH})
+
+  set(LIBFUZZER_TEST_RUNTIME RTFuzzerTest.${arch})
+  if(APPLE)
+    set(LIBFUZZER_TEST_RUNTIME_OBJECTS
+      $<TARGET_OBJECTS:RTfuzzer.osx>)
+  else()
+    set(LIBFUZZER_TEST_RUNTIME_OBJECTS
+      $<TARGET_OBJECTS:RTfuzzer.${arch}>)
+  endif()
+  add_library(${LIBFUZZER_TEST_RUNTIME} STATIC
+    ${LIBFUZZER_TEST_RUNTIME_OBJECTS})
+  set_target_properties(${LIBFUZZER_TEST_RUNTIME} PROPERTIES
+    ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+    FOLDER "Compiler-RT Runtime tests")
+
+  if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH)
+    set(LIBFUZZER_TEST_RUNTIME_DEPS libcxx_fuzzer_${arch}-build)
+    set(LIBFUZZER_TEST_RUNTIME_CFLAGS -isystem ${COMPILER_RT_LIBCXX_PATH}/include)
+    set(LIBFUZZER_TEST_RUNTIME_LINK_FLAGS ${LIBCXX_${arch}_PREFIX}/lib/libc++.a)
+  endif()
+
+  set(FuzzerTestObjects)
+  generate_compiler_rt_tests(FuzzerTestObjects
+    FuzzerUnitTests "Fuzzer-${arch}-Test" ${arch}
+    SOURCES FuzzerUnittest.cpp ${COMPILER_RT_GTEST_SOURCE}
+    RUNTIME ${LIBFUZZER_TEST_RUNTIME}
+    DEPS gtest ${LIBFUZZER_TEST_RUNTIME_DEPS}
+    CFLAGS ${LIBFUZZER_UNITTEST_CFLAGS} ${LIBFUZZER_TEST_RUNTIME_CFLAGS}
+    LINK_FLAGS ${LIBFUZZER_UNITTEST_LINK_FLAGS} ${LIBFUZZER_TEST_RUNTIME_LINK_FLAGS})
+  set_target_properties(FuzzerUnitTests PROPERTIES
+    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
 endif()
-
-set(FuzzerTestObjects)
-generate_compiler_rt_tests(FuzzerTestObjects
-  FuzzerUnitTests "Fuzzer-${arch}-Test" ${arch}
-  SOURCES FuzzerUnittest.cpp ${COMPILER_RT_GTEST_SOURCE}
-  RUNTIME ${LIBFUZZER_TEST_RUNTIME}
-  DEPS gtest ${LIBFUZZER_TEST_RUNTIME_DEPS}
-  CFLAGS ${LIBFUZZER_UNITTEST_CFLAGS} ${LIBFUZZER_TEST_RUNTIME_CFLAGS}
-  LINK_FLAGS ${LIBFUZZER_UNITTEST_LINK_FLAGS} ${LIBFUZZER_TEST_RUNTIME_LINK_FLAGS})
-set_target_properties(FuzzerUnitTests PROPERTIES
-  RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})