[compiler-rt][cmake] Attempt to fix build race condition

[msearles]

Summary

Fix for https://bugs.llvm.org/show_bug.cgi?id=26054

There was code which purported to work around a bug in cmake version
2. This involved creating a dummy.cpp file which had dependencies on
the '.vers' script.

Now that cmake version 3.13.4 is the minimum version of cmake this
work-around is removed and a straight forward dependency on the PHONY
target clang_rt.asan-dynamic-${arch}-version-list is introduced.

This appears to work with both GNUmake and ninja as targets.

compiler-rt/lib/asan/CMakeLists.txt

if(NOT APPLE)
   add_compiler_rt_object_libraries(RTAsan_preinit
     ARCHS ${ASAN_SUPPORTED_ARCH}
     SOURCES ${ASAN_PREINIT_SOURCES}
     ADDITIONAL_HEADERS ${ASAN_HEADERS}
     CFLAGS ${ASAN_CFLAGS}
     DEFS ${ASAN_COMMON_DEFINITIONS}
     DEPS ${ASAN_DEPS})
 
-  file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/dummy.cpp "")
-  add_compiler_rt_object_libraries(RTAsan_dynamic_version_script_dummy
-    ARCHS ${ASAN_SUPPORTED_ARCH}
-    SOURCES ${CMAKE_CURRENT_BINARY_DIR}/dummy.cpp
-    CFLAGS ${ASAN_DYNAMIC_CFLAGS}
-    DEFS ${ASAN_DYNAMIC_DEFINITIONS}
-    DEPS ${ASAN_DEPS})
 endif()
 
 # Build ASan runtimes shipped with Clang.
 add_compiler_rt_component(asan)
 
 if(APPLE)
   add_weak_symbols("asan" WEAK_SYMBOL_LINK_FLAGS)
   add_weak_symbols("lsan" WEAK_SYMBOL_LINK_FLAGS)
add_compiler_rt_runtime(clang_rt.asan-preinit
     ARCHS ${ASAN_SUPPORTED_ARCH}
     OBJECT_LIBS RTAsan_preinit
     CFLAGS ${ASAN_CFLAGS}
     DEFS ${ASAN_COMMON_DEFINITIONS}
     PARENT_TARGET asan)
 
   foreach(arch ${ASAN_SUPPORTED_ARCH})
     if (COMPILER_RT_HAS_VERSION_SCRIPT)
+      # adds a custom target clang_rt.asan-dynamic-${arch}-version-list
+      # which depends on vers = ${CMAKE_CURRENT_BINARY_DIR}/clang_rt.asan-dynamic-${arch}.vers
+      # and runs python to generate it.
       add_sanitizer_rt_version_list(clang_rt.asan-dynamic-${arch}
                                     LIBS clang_rt.asan-${arch} clang_rt.asan_cxx-${arch}
                                     EXTRA asan.syms.extra)
       set(VERSION_SCRIPT_FLAG
            -Wl,--version-script,${CMAKE_CURRENT_BINARY_DIR}/clang_rt.asan-dynamic-${arch}.vers)
       # The Solaris 11.4 linker supports a subset of GNU ld version scripts,
       # but requires a special option to enable it.
       if (COMPILER_RT_HAS_GNU_VERSION_SCRIPT_COMPAT)
           list(APPEND VERSION_SCRIPT_FLAG -Wl,-z,gnu-version-script-compat)
       endif()
-      set_property(SOURCE
-        ${CMAKE_CURRENT_BINARY_DIR}/dummy.cpp
-        APPEND PROPERTY
-        OBJECT_DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/clang_rt.asan-dynamic-${arch}.vers)
     else()
       set(VERSION_SCRIPT_FLAG)
     endif()
 
     set(ASAN_DYNAMIC_WEAK_INTERCEPTION)
     if (WIN32)
       add_compiler_rt_object_libraries(AsanWeakInterception
         ${SANITIZER_COMMON_SUPPORTED_OS}
if (WIN32)
           SanitizerCommonWeakInterception)
     endif()
 
     add_compiler_rt_runtime(clang_rt.asan
       SHARED
       ARCHS ${arch}
       OBJECT_LIBS ${ASAN_COMMON_RUNTIME_OBJECT_LIBS}
               RTAsan_dynamic
-              # The only purpose of RTAsan_dynamic_version_script_dummy is to
-              # carry a dependency of the shared runtime on the version script.
-              # Replacing it with a straightforward
-              # add_dependencies(clang_rt.asan-dynamic-${arch} clang_rt.asan-dynamic-${arch}-version-list)
-              # generates an order-only dependency in ninja.
-              RTAsan_dynamic_version_script_dummy
               RTUbsan_cxx
               ${ASAN_DYNAMIC_WEAK_INTERCEPTION}
       CFLAGS ${ASAN_DYNAMIC_CFLAGS}
       LINK_FLAGS ${ASAN_DYNAMIC_LINK_FLAGS}
                 ${VERSION_SCRIPT_FLAG}
       LINK_LIBS ${ASAN_DYNAMIC_LIBS}
       DEFS ${ASAN_DYNAMIC_DEFINITIONS}
       PARENT_TARGET asan)
+    add_dependencies(clang_rt.asan-dynamic-${arch} clang_rt.asan-dynamic-${arch}-version-list)
 
     if (SANITIZER_USE_SYMBOLS AND NOT ${arch} STREQUAL "i386")
       add_sanitizer_rt_symbols(clang_rt.asan_cxx
         ARCHS ${arch})
       add_dependencies(asan clang_rt.asan_cxx-${arch}-symbols)
       add_sanitizer_rt_symbols(clang_rt.asan
         ARCHS ${arch}
         EXTRA asan.syms.extra)