[XRay] Set an explicit dependency on libc++ when needed

[phosek]

Summary

When XRay is being built as part of the just built compiler together
with libc++ as part of the runtimes build, we need an explicit
dependency from XRay to libc++ to make sure that the library is
available by the time we start building XRay.

[dberris]

LGTM -- thanks!

compiler-rt/cmake/Modules/AddCompilerRT.cmake

 # Tries to add an "object library" target for a given list of OSs and/or
 # architectures with name "<name>.<arch>" for non-Darwin platforms if
 # architecture can be targeted, and "<name>.<os>" for Darwin platforms.
 # add_compiler_rt_object_libraries(<name>
 #                                  OS <os names>
 #                                  ARCHS <architectures>
 #                                  SOURCES <source files>
 #                                  CFLAGS <compile flags>
-#                                  DEFS <compile definitions>)
+#                                  DEFS <compile definitions>
+#                                  DEPS <dependencies>)
 function(add_compiler_rt_object_libraries name)
-  cmake_parse_arguments(LIB "" "" "OS;ARCHS;SOURCES;CFLAGS;DEFS" ${ARGN})
+  cmake_parse_arguments(LIB "" "" "OS;ARCHS;SOURCES;CFLAGS;DEFS;DEPS" ${ARGN})
   set(libnames)
   if(APPLE)
     foreach(os ${LIB_OS})
       set(libname "${name}.${os}")
       set(libnames ${libnames} ${libname})
       set(extra_cflags_${libname} ${DARWIN_${os}_CFLAGS})
       list_intersect(LIB_ARCHS_${libname} DARWIN_${os}_ARCHS LIB_ARCHS)
     endforeach()
   else()
     foreach(arch ${LIB_ARCHS})
       set(libname "${name}.${arch}")
       set(libnames ${libnames} ${libname})
       set(extra_cflags_${libname} ${TARGET_${arch}_CFLAGS})
       if(NOT CAN_TARGET_${arch})
         message(FATAL_ERROR "Architecture ${arch} can't be targeted")
         return()
       endif()
     endforeach()
   endif()
 
   foreach(libname ${libnames})
     add_library(${libname} OBJECT ${LIB_SOURCES})
+    if(LIB_DEPS)
+      add_dependencies(${libname} ${LIB_DEPS})
+    endif()
 
     # Strip out -msse3 if this isn't macOS.
     set(target_flags ${LIB_CFLAGS})
     if(APPLE AND NOT "${libname}" MATCHES ".*\.osx.*")
       list(REMOVE_ITEM target_flags "-msse3")
     endif()
 
     set_target_compile_flags(${libname}

compiler-rt/lib/xray/CMakeLists.txt

append_list_if(
   COMPILER_RT_BUILD_XRAY_NO_PREINIT XRAY_NO_PREINIT XRAY_COMMON_DEFINITIONS)
 
 add_compiler_rt_component(xray)
 
 set(XRAY_COMMON_RUNTIME_OBJECT_LIBS
     RTSanitizerCommon
     RTSanitizerCommonLibc)
 
+if (CLANG_DEFAULT_CXX_STDLIB STREQUAL "libc++" AND (TARGET cxx OR HAVE_LIBCXX))
+  set(XRAY_DEPS "cxx")
+endif()
+
 if (APPLE)
   set(XRAY_LINK_LIBS ${SANITIZER_COMMON_LINK_LIBS})
   add_asm_sources(XRAY_ASM_SOURCES xray_trampoline_x86_64.S)
 
   add_weak_symbols("sanitizer_common" WEAK_SYMBOL_LINK_FLAGS)
   add_weak_symbols("xray" WEAK_SYMBOL_LINK_FLAGS)
 
   add_compiler_rt_object_libraries(RTXray
     OS ${XRAY_SUPPORTED_OS}
     ARCHS ${XRAY_SUPPORTED_ARCH}
     SOURCES ${x86_64_SOURCES}
     CFLAGS ${XRAY_CFLAGS}
-    DEFS ${XRAY_COMMON_DEFINITIONS})
+    DEFS ${XRAY_COMMON_DEFINITIONS}
+    DEPS ${XRAY_DEPS})
   add_compiler_rt_object_libraries(RTXrayFDR
     OS ${XRAY_SUPPORTED_OS}
     ARCHS ${XRAY_SUPPORTED_ARCH}
     SOURCES ${XRAY_FDR_MODE_SOURCES}
     CFLAGS ${XRAY_CFLAGS}
-    DEFS ${XRAY_COMMON_DEFINITIONS})
+    DEFS ${XRAY_COMMON_DEFINITIONS}
+    DEPS ${XRAY_DEPS})
   add_compiler_rt_object_libraries(RTXrayBASIC
     OS ${XRAY_SUPPORTED_OS}
     ARCHS ${XRAY_SUPPORTED_ARCH}
     SOURCES ${XRAY_BASIC_MODE_SOURCES}
     CFLAGS ${XRAY_CFLAGS}
-    DEFS ${XRAY_COMMON_DEFINITIONS})
+    DEFS ${XRAY_COMMON_DEFINITIONS}
+    DEPS ${XRAY_DEPS})
   add_compiler_rt_object_libraries(RTXrayPROFILING
     OS ${XRAY_SUPPORTED_OS}
     ARCHS ${XRAY_SUPPORTED_ARCH}
     SOURCES ${XRAY_PROFILING_MODE_SOURCES}
     CFLAGS ${XRAY_CFLAGS}
-    DEFS ${XRAY_COMMON_DEFINITIONS})
+    DEFS ${XRAY_COMMON_DEFINITIONS}
+    DEPS ${XRAY_DEPS})
 
   # We only support running on osx for now.
   add_compiler_rt_runtime(clang_rt.xray
     STATIC
     OS ${XRAY_SUPPORTED_OS}
     ARCHS ${XRAY_SUPPORTED_ARCH}
     OBJECT_LIBS RTXray
                 RTSanitizerCommon

 else() # not Apple
   foreach(arch ${XRAY_SUPPORTED_ARCH})
     if(NOT CAN_TARGET_${arch})
       continue()
     endif()
     add_compiler_rt_object_libraries(RTXray
       ARCHS ${arch}
       SOURCES ${XRAY_SOURCES} ${${arch}_SOURCES} CFLAGS ${XRAY_CFLAGS}
-      DEFS ${XRAY_COMMON_DEFINITIONS})
+      DEFS ${XRAY_COMMON_DEFINITIONS}
+      DEPS ${XRAY_DEPS})
     add_compiler_rt_object_libraries(RTXrayFDR
       ARCHS ${arch}
       SOURCES ${XRAY_FDR_MODE_SOURCES} CFLAGS ${XRAY_CFLAGS}
-      DEFS ${XRAY_COMMON_DEFINITIONS})
+      DEFS ${XRAY_COMMON_DEFINITIONS}
+      DEPS ${XRAY_DEPS})
     add_compiler_rt_object_libraries(RTXrayBASIC
       ARCHS ${arch}
       SOURCES ${XRAY_BASIC_MODE_SOURCES} CFLAGS ${XRAY_CFLAGS}
-      DEFS ${XRAY_COMMON_DEFINITIONS})
+      DEFS ${XRAY_COMMON_DEFINITIONS}
+      DEPS ${XRAY_DEPS})
     add_compiler_rt_object_libraries(RTXrayPROFILING
       ARCHS ${arch}
       SOURCES ${XRAY_PROFILING_MODE_SOURCES} CFLAGS ${XRAY_CFLAGS}
-      DEFS ${XRAY_COMMON_DEFINITIONS})
+      DEFS ${XRAY_COMMON_DEFINITIONS}
+      DEPS ${XRAY_DEPS})
 
     # Common XRay archive for instrumented binaries.
     add_compiler_rt_runtime(clang_rt.xray
      STATIC
      ARCHS ${arch}
      CFLAGS ${XRAY_CFLAGS}
      DEFS ${XRAY_COMMON_DEFINITIONS}
      OBJECT_LIBS ${XRAY_COMMON_RUNTIME_OBJECT_LIBS} RTXray