Revert "[libc++] Use CMake interface targets to setup benchmark flags"

This reverts commit da0592e4c8.

Reverting because this is incompatible with cmake 3.13.5, with the
minimum supported version being 3.13.4.

See https://luci-milo.appspot.com/p/fuchsia/builders/ci/clang-linux-x64/b8871967816877544224.

libcxx/benchmarks/CMakeLists.txt

@@ -70,33 +70,57 @@ set(BENCHMARK_OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR})
 set(BENCHMARK_LIBCXX_INSTALL ${CMAKE_CURRENT_BINARY_DIR}/benchmark-libcxx)
 set(BENCHMARK_NATIVE_INSTALL ${CMAKE_CURRENT_BINARY_DIR}/benchmark-native)
 
-add_library(cxx-benchmarks-flags INTERFACE)
-target_compile_features(cxx-benchmarks-flags INTERFACE cxx_std_17)
-target_compile_options(cxx-benchmarks-flags INTERFACE -O2 -fsized-deallocation)
-target_include_directories(cxx-benchmarks-flags INTERFACE ${BENCHMARK_LIBCXX_INSTALL}/include
-                                                INTERFACE ${LIBCXX_SOURCE_DIR}/test/support)
-
-add_library(cxx-benchmarks-flags-native INTERFACE)
-target_link_libraries(cxx-benchmarks-flags-native INTERFACE cxx-benchmarks-flags)
-target_compile_options(cxx-benchmarks-flags-native INTERFACE ${BENCHMARK_NATIVE_TARGET_FLAGS})
-target_link_options(cxx-benchmarks-flags-native INTERFACE ${BENCHMARK_NATIVE_TARGET_FLAGS} -L${BENCHMARK_NATIVE_INSTALL}/lib)
-if (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++")
-  find_library(LIBSTDCXX_FILESYSTEM_TEST stdc++fs
-    PATHS ${LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN}
-    PATH_SUFFIXES lib lib64
-    DOC "The libstdc++ filesystem library used by the benchmarks"
-  )
-  if (LIBSTDCXX_FILESYSTEM_TEST)
-    target_link_libraries(cxx-benchmarks-flags-native INTERFACE "-lstdc++fs")
-  endif()
+check_flag_supported("-std=c++17")
+mangle_name("LIBCXX_SUPPORTS_STD_EQ_c++17_FLAG" BENCHMARK_SUPPORTS_STD_CXX17_FLAG)
+if (${BENCHMARK_SUPPORTS_STD_CXX17_FLAG})
+  set(BENCHMARK_DIALECT_FLAG "-std=c++17")
 else()
-  target_link_libraries(cxx-benchmarks-flags-native INTERFACE -lc++fs -lc++experimental)
+  # If the compiler doesn't support -std=c++17, attempt to fall back to -std=c++1z while still
+  # requiring C++17 language features.
+  set(BENCHMARK_DIALECT_FLAG "-std=c++1z")
 endif()
 
-add_library(cxx-benchmarks-flags-libcxx INTERFACE)
-target_link_libraries(cxx-benchmarks-flags-libcxx INTERFACE cxx-benchmarks-flags)
-target_compile_options(cxx-benchmarks-flags-libcxx INTERFACE ${SANITIZER_FLAGS} -Wno-user-defined-literals)
-target_link_options(cxx-benchmarks-flags-libcxx INTERFACE -nodefaultlibs -L${BENCHMARK_LIBCXX_INSTALL}/lib/ ${SANITIZER_FLAGS})
+set(BENCHMARK_TEST_COMPILE_FLAGS
+    ${BENCHMARK_DIALECT_FLAG} -O2
+    -fsized-deallocation
+    -I${BENCHMARK_LIBCXX_INSTALL}/include
+    -I${LIBCXX_SOURCE_DIR}/test/support
+)
+set(BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS
+    ${BENCHMARK_TEST_COMPILE_FLAGS}
+    ${SANITIZER_FLAGS}
+    -Wno-user-defined-literals
+)
+
+set(BENCHMARK_TEST_LIBCXX_LINK_FLAGS
+    -nodefaultlibs
+    -L${BENCHMARK_LIBCXX_INSTALL}/lib/
+    ${SANITIZER_FLAGS}
+)
+set(BENCHMARK_TEST_NATIVE_COMPILE_FLAGS
+  ${BENCHMARK_NATIVE_TARGET_FLAGS}
+  ${BENCHMARK_TEST_COMPILE_FLAGS}
+)
+set(BENCHMARK_TEST_NATIVE_LINK_FLAGS
+    ${BENCHMARK_NATIVE_TARGET_FLAGS}
+    -L${BENCHMARK_NATIVE_INSTALL}/lib
+)
+split_list(BENCHMARK_TEST_COMPILE_FLAGS)
+split_list(BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS)
+split_list(BENCHMARK_TEST_LIBCXX_LINK_FLAGS)
+split_list(BENCHMARK_TEST_NATIVE_COMPILE_FLAGS)
+split_list(BENCHMARK_TEST_NATIVE_LINK_FLAGS)
+
+if (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++")
+  find_library(LIBSTDCXX_FILESYSTEM_TEST stdc++fs
+        PATHS ${LIBCXX_BENCHMARK_NATIVE_GCC_TOOLCHAIN}
+        PATH_SUFFIXES lib lib64
+        DOC "The libstdc++ filesystem library used by the benchmarks"
+    )
+    if (NOT "${LIBSTDCXX_FILESYSTEM_TEST}" STREQUAL "LIBSTDCXX_FILESYSTEM_TEST-NOTFOUND")
+      set(LIBSTDCXX_FILESYSTEM_LIB "stdc++fs")
+    endif()
+endif()
 
 set(libcxx_benchmark_targets)
 
@@ -104,7 +128,6 @@ function(add_benchmark_test name source_file)
   set(libcxx_target ${name}_libcxx)
   list(APPEND libcxx_benchmark_targets ${libcxx_target})
   add_executable(${libcxx_target} EXCLUDE_FROM_ALL ${source_file})
-  target_link_libraries(${libcxx_target} PRIVATE cxx-benchmarks-flags-libcxx)
   add_dependencies(${libcxx_target} cxx google-benchmark-libcxx)
   add_dependencies(cxx-benchmarks ${libcxx_target})
   if (LIBCXX_ENABLE_SHARED)
@@ -122,15 +145,25 @@ function(add_benchmark_test name source_file)
   set_target_properties(${libcxx_target}
     PROPERTIES
           OUTPUT_NAME "${name}.libcxx.out"
-          RUNTIME_OUTPUT_DIRECTORY "${BENCHMARK_OUTPUT_DIR}")
+          RUNTIME_OUTPUT_DIRECTORY "${BENCHMARK_OUTPUT_DIR}"
+          COMPILE_FLAGS "${BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS}"
+          LINK_FLAGS "${BENCHMARK_TEST_LIBCXX_LINK_FLAGS}")
   cxx_link_system_libraries(${libcxx_target})
   if (LIBCXX_BENCHMARK_NATIVE_STDLIB)
+    if (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++" AND NOT DEFINED LIBSTDCXX_FILESYSTEM_LIB
+        AND "${name}" STREQUAL "filesystem")
+      return()
+    endif()
     set(native_target ${name}_native)
     add_executable(${native_target} EXCLUDE_FROM_ALL ${source_file})
-    target_link_libraries(${native_target} PRIVATE cxx-benchmarks-flags-native)
     add_dependencies(${native_target} google-benchmark-native
                                       google-benchmark-libcxx)
     target_link_libraries(${native_target} PRIVATE -lbenchmark)
+    if (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libstdc++")
+      target_link_libraries(${native_target} PRIVATE ${LIBSTDCXX_FILESYSTEM_LIB})
+    elseif (LIBCXX_BENCHMARK_NATIVE_STDLIB STREQUAL "libc++")
+      target_link_libraries(${native_target} PRIVATE -lc++fs -lc++experimental)
+    endif()
     if (LIBCXX_HAS_PTHREAD_LIB)
       target_link_libraries(${native_target} PRIVATE -pthread)
     endif()
@@ -138,7 +171,10 @@ function(add_benchmark_test name source_file)
     set_target_properties(${native_target}
       PROPERTIES
           OUTPUT_NAME "${name}.native.out"
-          RUNTIME_OUTPUT_DIRECTORY "${BENCHMARK_OUTPUT_DIR}")
+          RUNTIME_OUTPUT_DIRECTORY "${BENCHMARK_OUTPUT_DIR}"
+          INCLUDE_DIRECTORIES ""
+          COMPILE_FLAGS "${BENCHMARK_TEST_NATIVE_COMPILE_FLAGS}"
+          LINK_FLAGS "${BENCHMARK_TEST_NATIVE_LINK_FLAGS}")
   endif()
 endfunction()